that follows 60 minutes and the good wife and the mentalist. >> similar line to the putt jordan spieth had on the first playoff hole. he got to see that putt. that always helps. confirmation to maybe hit it a fraction firmer than it looks. >> he made the same mistake, back up the hill you see. a big chance for zach johnson to efend his title. huge hometown support. not like they are pulling against the other two. they are very popular as well.

zach and steve stricker here are the menu must say. >> he won in a playoff last year. such a big win for him. >> this is where wearing that green jacket comes in handy sometimes, just he experience. >> won twice at colonial. trying to win twice here at the john deere. looking for his 10th pga tour victory including the 2007 win at the masters.

so close on the last two holes. last two times they played the 18th. 16th hole will be the next to play the par 3. >> everyone making their way over to the par 3, 16th. this is where the playoff will resume. jordan spieth would like to join them but he has to make this though.

let's see how close it came to ending things. >> wasn't far way, was it. just a little right of center, this one. beautiful. >> i don't think any moment is too big for this guy >> >> really handling this well. >> he is going to be fun to watch over the coming years. >> you would have to think. just an immense talent. and a fine young

ellow as well. >> this is for hearn to continue as well. the man from canada says do not forget about me. he will head to the 16th also. so the third hole of sudden death. zach johnson had a chance to end it. he thought he had done it. but jordan spieth able to stay in it. on we go. as your trusted technology partner, you can do just that. with our visionary cloud infrastructure, global broadband network and custom communications solutions,

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>> so back over to the signature hole, the 16th. rock river there along the players eft. great golf hole. >> beautiful hole. just beyond that bunker. >> somewhere between a pitching wedge and an 8-iron for all of the players. some of them just feeding an 8-iron in but most a full wedge or a nine. >> zach looks like he had a chance to really seize control in the final round but could not make a birdie. all of those consecutive pars. >> 147 yards.

>> jordan spieth, second to go. david hearn third to play. >> here is the strategy, sudden death on a par 3, any different. >> i would think on a hole like this one, bill, it is a good question. i would be trying to knock it in and make the birdie. i think you need a birdie to stay in it. i think anyone that makes par here they are probably not going forward. >> zach hasn't had a birdie here all week. >> zach has a 9-iron out. >> parred the 16th every time he has played it. >> perfect club.

>> starting to head right. not bad. perfect club. good distance. >> you can tell by his reaction he wasn't as excited as the gallery. he wished he could have gotten a little closer. >> saying to his caddie, good, solid pitching wedge. last time i hit a nine. i like the wedge. >> david, you like this kids'

composeure? >> do i ever. i mean he has a great balance of aggression and temper. a fantastic attitude to go with it. love him. a breeze pushing the balls to the right. >> asking for it to go. breeze coming off the bank there off of the rock river, can't feel it back in the trees. >> let's see what david hearn can do. >> he as nine. >> third birdies this week. and a bogey at

16. >> made a good putt for birdie, really. >> take a little more club, a -iron. right at it. so david hearn trying to win for the first time on the pga tour and join the field at the open championship has a look at birdie. sudden death at the john deere classic. when you experience something great, you want to share it. with everyone. that's why more customers recommend verizon, america's largest 4g lte network.

>> back. third hole of udden death. jordan spieth played the par 3's awfully well. >> has he ever. >> he has the bigger challenge among the three. >> he is in a situation here where he has to

feel that david hearn is going to make his for the birdie or zach. one of them will make it. at the same time if they don't and he blows this chip or long putt beyond the hole or leaves himself too long for the par can put himself out of it with a bogey. so he has two minds for the shot. i do make sure i get it close and secure it with a three or do i go at it with reckless abandon and go for the two. as a 19-year-old david what do you think a 19 would be thinking about the two and the aggression? >> yeah. i think so. you know you have o think one of these guys will make it. so you have to et it there. >> i went seven holes in a playoff once. the week before i won the open championship. >> longest

playoff in pga tour history was the motor city hope. they went at it until dark ness and were declared co-winners. >> 11 holes, eez. >> let's see what jordan can do. >> putting through the shadows. t the flag out reat effort. >> he thought it would break a little more. i think he had the line he wanted. >> the playoff went to darkness and i was in it i would find a way to hit the other guy with a 2 x 4. nobody would otice.

>> zach is already on that charter to the open championship. david hearn would love to book package. there is our friend sam allen, chairman of the c.e.o. with the group in the playoff. such a great host. he was a pretty good player back in the day. the golf team at purdue. >> a big supporter of the evan scholar as well as the tournament as well. reat initiative. >> funny putt here. you know they can trick you into not hitting it hard enough. i would be surprised if he does not give his one a scare.

exactly david. you think it will turn down towards the river and it does not. a tap-in par. > it got me too. >> what a big moment this is for mr. hearn. trying to open up into the open championship and earn his first pga tour victory. he came in with only one top 10 this year. what a week he has had. >> i read this one left edge and now i am thinking it may not go. he holed a good putt here in regulation. that is a good feeling for him. good memories. telling him to go with what you

think. if you don't go with what you think you won't hit a good putt. take your time reading it. when you are over just stick with that read. see it going in and make the stroke. a lot of trust involved right now. a lot of pressure. a good, deep reath. so the playoff will continue.

so on they go. due to the length of today's play we have to conclude coverage for our east and central time zone cbs station. viewers in those areas can tune to golf channel for continuing tournament. for those on the west coast we return with more action after this message as we show you the lineup tonight on cbs beginning with 60 minutes and a new episode of big brother and the good wife and the mentalist. for those of you leaving us so long from the quad cities. the playoff continues at the john deere classic.

captioning funded by cbs and ford-- built for the road ahead. >> kroft: in 45 years of "60 minutes," we have never interviewed a serial killer until now. do you consider yourself a serial killer? >> i mean, i guess it depends upon a person's definition. if it's more than one and it's a pattern, i guess then, yes. >> kroft: not only is he a serial killer, he is one of the most prolific serial killers in u.s. history. charles cullen admits to as many as 40 murders though some suspect it's a lot more. they took place over 16 years in seven different hospitals where cullen, a critical care nurse, gave unsuspecting patients

lethal doses of powerful drugs. >> we'll never know how many people charlie cullen killed. >> kroft: how many do you think? i would be very surprised as would anyone i've spoken to with any knowledge of this case if it not in the multiple hundreds. >> stahl: madagascar is a paradise of plants and animals found nowhere else in the world. like wide-eyed lemurs, chameleons that sparkle with color. geckos that hide in plain sight and more than 200 kinds of frogs, but we were searching for a rare creature that has roamed the earth for more than 200 million years. >> they found one. >> i'm steve kroft. >> i'm leslie stahl. >> i'm morley safer. >> i'm bob simon. >> i'm lara logan. >> i'm scott pelley. those stories tonight on "60 minutes." "i'm part of an american success story,"

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>> kroft: tonight, you're going to come face-to-face with a serial killer, one of the most prolific in u.s. history. serial killers don't usually talk to reporters. in fact, this story, which first ran in april, was the first time in the 45 years of "60 minutes" that we ever interviewed one. charles cullen was a critical care nurse who admits to killing up to 40 people. some suspect it was a lot more. the murders took place over 16 years in seven different hospitals.

there were suspicions at nearly all of them that cullen was harming patients, yet none of them passed that information on to subsequent employers. newspaper headlines called him "the angel of death," but, as you will see, charles cullen was no mercy killer. until we interviewed him four months ago, he had never spoken publicly about his crimes, never tried to explain why he did it or even express remorse to the families of victims when he finally faced them in court. >> thomas strenko: this monster didn't even know us or our son but had the audacity to end his life. >> richard stoeker: i'd like to tell you a little about my mother that you murdered. you don't even have the guts to look this way, do you? >> clara hardgrove: charles, why don't you look up at us? i'd like to show you what you did to our children. this is their dad in his coffin. how do you like that? >> kroft: this was the scene seven years ago at the somerset county courthouse in new jersey as charles cullen sat through his sentencing hearing, refusing to speak or even acknowledge the family members of people he had

murdered. even the judge was exasperated. >> judge paul armstrong: mr. cullen, i asked you a question. why is it that you have chosen not to address the court? can you hear me, mr. cullen? >> kroft: he's kept that silence behind the walls of the new jersey state prison in trenton, where he is in protective custody to keep him safe from other inmates. protecting himself from his own demons has been more difficult, as we found out when we sat down across from him in a cramped cubicle separated by a thick layer of glass to talk about the people he's killed. is 40 an arbitrary number? >> cullen: 40 is an estimate. i gave a number between 30 and 40. i think i have identified, you know, most of them. >> kroft: look, you pled guilty to murder, but you don't use that word. >> cullen: i think that i had a lot of trouble accepting that word for a long time.

i accept that that's what it is. >> kroft: do you consider yourself a serial killer? >> cullen: i mean, i guess it depends upon a person's definition. if it's more than one and it's a pattern, i guess, then, yes. >> kroft: in cullen's case, all his victims were patients assigned to hospital units where he worked as a nurse. they ranged in age from 21 to 91. some were critically ill. others were ready to be discharged when cullen injected them with drugs that would kill them. it was a pattern that began 26 years ago at st. barnabas medical center in livingston, new jersey, cullen's very first nursing job. >> cullen: i worked on the burn unit, so, i mean, there was a lot of pain, a lot of suffering. and i didn't cope with that as well as i thought i would. >> kroft: and that was the first place that you gave someone medication that caused them to die?

>> cullen: yes. >> kroft: the patient was john yengo, a judge from new jersey who was suffering from a severe case of sunburn until cullen injected him with a fatal overdose of lidocaine. do you remember the person? >> cullen: i mean, i remember one, and that's the only person i've been able to identify. >> kroft: but there could have been more. st. barnabas didn't know about the patient cullen murdered, but it did suspect him of trying to kill or harm a half dozen other patients by randomly and repeatedly poisoning bags of saline solution. >> charles graebar: someone was spiking i.v. bags with insulin in the store room. >> kroft: charles graeber, a new york writer as well as a former medical student and researcher, has spent seven years investigating cullen's murders for a new book called "the good nurse." graeber says a number of patients at st. barnabas went into insulin shock and nearly died. >> graeber: he was the main suspect for poisoning random bags of saline. if you talked to the investigators there, they'll tell you, "cullen was our man. we knew he was dirty."

they couldn't prove anything. it's all circumstantial. >> kroft: they fire him? >> graeber: he moved on. >> kroft: when cullen left the hospital, the insulin overdoses stopped. >> cullen: at st. barnabas, they could've had my license investigated and probably revoked at that point in time. >> kroft: should they have? >> cullen: should they have? yes. >> kroft: but instead of ending charles cullen's nursing career, st. barnabas marked the beginning of a 16-year killing spree. cullen would work at eight other hospitals and be suspected of harming patients at six of them, but those suspicions never reached subsequent employers and cullen continued to murder patients with virtual impunity. in 1993, prosecutors investigated cullen for murdering 91-year-old helen dean. an autopsy tested for nearly 100 medications but not the one cullen used to kill her, a powerful drug called digoxin, or

dig for short. it was cullen's first weapon of choice. why did you like dig? >> cullen: dig, you know, it was a very powerful cardiac medication. >> kroft: what does it do to someone? >> cullen: in small amounts, it slows the heart rate down. in larger amounts, it can cause what's called complete heart block. and then, the heart is very irregular. and, you know, it can cause death. it does cause death in large amounts. >> kroft: it was also readily available in critical care units, and cullen figured out ways to conceal his digoxin withdrawals from an automatic drug dispensary system called pyxis, which required nurses to type in the name of the patient and the drug to be administered. >> cullen: i wouldn't go in for dig. i would go under tylenol or another medication that would be in the same drawer. so, you know, there was no record of me going in for dig other than the fact that, you

know, it was in the same drawer. >> kroft: how did you choose who you're going to give this medication to? >> cullen: it's difficult for me to go back in time and think about what things were running through my mind at the time. >> kroft: was it personal? >> cullen: no, no. >> kroft: did you get pleasure out of it? satisfaction? >> cullen: no. i thought that, that people weren't suffering anymore. so, in a sense, i thought i was helping. >> kroft: cullen suggested several times that his actions were merciful, but the evidence doesn't support it. 60-year-old elenor stoecker, an asthma patient, was recovering and in no pain when cullen administered a fatal digoxin overdose. college student michael strenko, who suffered from an auto immune disease, was recovering from what his parents called routine surgery to remove his spleen. >> mary strenko: my heart, it aches for my son.

it bleeds for my son. >> thomas strenko: we vividly remember charles cullen walking into the waiting room. he looked us right in the eye and stated how michael was gravely ill and people don't make it. and my wife told cullen, "that's enough. you can leave now." we're haunted by the memory of charles cullen coming to the waiting room to get our reaction. >> kroft: there were people that you caused to die who were not near death and not suffering that much. >> cullen: you know, again, you know, i mean, my goal here isn't to justify. you know, what i did there is no justification. i just think that the only thing i can say is that i felt overwhelmed at the time. >> kroft: can you give us anything?

can you give the families anything? any explanation for how this happened and why this happened? >> cullen: like i said, i... i can't... i just can't say that. it was more or less, you know, it felt like i needed to do something, and i... i did. and that's not an answer to anything. >> kroft: charles cullen was the youngest of eight children and grew up poor on this street in west orange, new jersey, protected by his mother. cullen was 17 when she died. he tried to kill himself. he spent six years in the navy, most of them as a missile technician on a nuclear submarine. he was miserable, felt bullied, tried to kill himself again. after receiving a general discharge, he decided to take up nursing.

he got married and started a family, but it all went sour. a messy divorce, custody battles, bankruptcy, heavy drinking, more half-hearted suicide attempts and trips to the psychiatric ward-- that was charles cullen's state of mind when he was killing people and on the night he finally confessed to the murders. >> cullen: i tried to kill myself throughout my life because i never really liked being who i was. because i didn't think i was worthy of anything. >> graeber: it was never about anyone but charlie cullen. he did what he did because of his own needs, his own compulsions. >> kroft: author charles graeber interviewed cullen more than a dozen times for his book, and he remembers seeing words like "paranoid," "major depression," "hostile," "passive-aggressive" and "anti-social" on psychiatric reports. >> graeber: he sees himself as a

victim, and, as a victim, he's entitled to lash out in any way he wants to make things right. if that means killing patients, anything justifies his victimhood. >> kroft: you said at one point that you thought it was about power and control. what do you mean? >> graeber: if the rest of his life was spinning out of control-- if he was losing custody, if he was feeling depressed, if his love life was in the toilet-- he could poison patients, he could save patients, he could make decisions. he had an arena in which he mattered and where his actions had definite consequences. >> kroft: here you have a person who tried to kill himself at least 20 times, who is in and out of psych wards, and, on some occasions, walked right out of the psych ward and right into a job as a critical care nurse.

>> graeber: right, he actually took a call asking him back on shift from a psych ward. >> kroft: why wouldn't the hospitals do some background checks? >> graeber: well, partially because they weren't required to and partially because there was a nursing shortage on. charlie cullen looked good. by the end of his career, he was a 16-year veteran. he had recommendations. and for a hospital to ask too much or say too much became a liability. you can't penalize a nurse for seeking counseling, for seeking treatment, for going to a rehab center successfully. and so, because of that, charlie hid in those shadows. >> kroft: when cullen was hired at st. luke's university hospital in bethlehem, pennsylvania, he had been fired or forced to resign from five other hospitals, yet none of this was in his file with the state nursing board. by his own count, cullen had already murdered 11 people, and he would kill at least five more at st. luke's. nurses were suspicious, there

were rumors about his past, and cullen was caught red-handed stealing lethal drugs. but instead of calling the police, st. luke's brought in a lawyer to confront cullen. do you think that they knew what you were doing at st. luke's? >> cullen: i think that they had a strong suspicion. >> kroft: did you expect to get caught? >> cullen: well, i think you can say i was caught at st. barnabas, and i was caught at st. luke's. there's no reason that i should've been a practicing nurse after that. >> kroft: they offered you some kind of a deal? >> cullen: they said, "if you resign, we'll give you neutral references," and i decided to go with that. >> kroft: what is it about this system and about hospitals that no one went to the police, no one really wanted to find out what was going on? they gave you an opportunity to leave. >> cullen: i think because it's a matter of worrying about lawsuits.

if they pointed out that there was a problem, they were going to be found liable for millions of dollars. they just saw it as a lot easier to not put themselves in a position of getting sued. >> kroft: after charles cullen was escorted out the door of st. luke's hospital with no consequences, one of the nurses called a friend at the pennsylvania state police with her suspicions, and an investigation was begun. by then, cullen had already found another job at the somerset medical center in new jersey. he would murder another 13 people there, but it would be his final stop. that story, when we come back. geoff: i'm the kind of guy who doesn't like being sold to. the last thing i want is to feel like someone is giving me a sales pitch, especially when it comes to my investments. you want a broker you can trust. a lot of guys at the other firms seemed more focused on selling than their clients. that's why i stopped working at my old brokerage and became a financial consultant with charles schwab.

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>> kroft: in september 2002, when charles cullen was hired as a critical care nurse at new jersey's somerset medical center, the hospital knew nothing about his dark past. it didn't know that he had been fired or forced to resign at a half a dozen hospitals, or that he'd been investigated by authorities for harming patients. and there was no reason to suspect that cullen had murdered five patients at his last job.

as we first reported in april, he was able to move from hospital to hospital without so much as a bad reference. cullen would kill another 13 people at somerset in 13 months and try and kill three more before two detectives, a state official and a female nurse finally connected the dots. you were under suspicion at st. luke's, yet you went off to somerset and kept doing exactly the same things. and it looks like, to me, that you wanted to get caught. >> cullen: i don't know. >> kroft: you don't know? >> cullen: because, you know, you're right. i mean, i continued, but i was also... i was also careful. i was also... deny it any time anybody would ask me. >> kroft: it was the suspicious death of a roman catholic priest

named florian gall that set in motion the events that would eventually expose charles cullen. reverend gall had died unexpectedly overnight while recovering from pneumonia, and the hospital discovered high levels of the heart drug digoxin in his blood. it was the second unexplained overdose in two weeks. >> dr. marcus: the blood levels were astronomical. they were way higher than you would ever shoot for by using the drug therapeutically. >> kroft: dr. steven marcus is the director of new jersey's poison control center. he heard about the digoxin overdoses when a pharmacist at somerset called his office asking for help with some dosage calculations. the pharmacist also confided that two more patients in the same unit had turned up with abnormally high levels of insulin. what's going through your mind? >> dr. marcus: my number one, two and three thought was that there was something malicious going on in the institution. >> kroft: in july of 2003, marcus set up an urgent

conference call with the hospital's medical director, dr. william cors, and taped the conversation in which he told the hospital to notify the authorities. >> dr. marcus: this is a police matter. >> dr. cors: what we're wrestling with is, you know, throwing the whole institution into chaos versus, you know, responsibility to, you know, protect patients from further harm. and we have been trying to investigate this to get some more information before we made any kind of rush to, you know, judgment. >> dr. marcus: if there is somebody out there that is purposely doing this to individuals at your hospital, we have a legal obligation to report this. >> dr. cors: okay. >> kroft: somerset medical center would eventually notify authorities, but it would take them three long months. do you know how many patients died between those... >> dr. marcus: no, i... i don't know the number. but i do know that there were some patients that died in between that, yes. >> kroft: five. >> dr. marcus: that we know of. >> kroft: but those...

>> dr. marcus: those five deaths will... i'll... i'll remember them the rest of my life. sorry. >> kroft: they didn't have to happen. >> dr. marcus: right. they... they should have been preventable, yes. >> kroft: it was october before somerset county detectives tim braun and daniel baldwin finally met with hospital officials. they were told about a half dozen incidents in the critical care unit. no one used the word "homicide." >> braun: they had dropped a couple names on us with regards to their own internal investigation that they claim to have conducted for several months. and they did provide us two names in particular but did not identify them as any type of suspect or anything like that. >> kroft: one of them was charles cullen? >> baldwin: yes. right. >> kroft: the detectives ran a routine background check on charles cullen and discovered that he had been arrested for stalking a female nurse and breaking into her apartment in

easton, pennsylvania. the file there also contained a post-it note saying that the pennsylvania state police had called just a few weeks earlier asking similar questions. detective baldwin called the trooper who made the inquiry and hit pay dirt. >> baldwin: after speaking with the trooper, he informed me that his agency had conducted an investigation on mr. cullen with the suspicion that he was murdering patients in pennsylvania, as well, that he was using digoxin to murder patients. >> kroft: and you found this out making two phone calls? >> baldwin: yes, basically. >> braun: that... that was it. >> kroft: did you think you had your man? >> baldwin: yes. >> braun: yes. >> kroft: but the detectives knew that proving it would be difficult. a number of law enforcement agencies had tried and failed. how helpful was the hospital in this investigation? >> braun: how helpful was the hospital? they were very helpful by answering court-issued subpoenas. that was the extent of their

cooperation. >> kroft: when the detectives asked to see computerized records from the automated drug dispensary in the critical care unit, they say the hospital told them that wasn't possible because drug dispensing machines only stored records for 30 days. they learned otherwise from the machine's manufacturer. they lied to you? >> braun: yes, they did. >> kroft: they didn't want to give you records that turned out to be crucial to your investigation. >> braun: yes. that's... that's correct. >> kroft: you think they tried to obstruct your investigation? >> braun: they didn't try to help it, that's for sure. >> kroft: when the detectives informed somerset that charles cullen was the target of their investigation, the hospital fired him not for harming patients; for lying on his job application. did you get the sense at somerset, for example, that any of your colleagues, any of nurses, any of the doctors knew what was going on? >> cullen: no. i mean, until, you know, of the

day i was fired, i mean, nobody gave me any indication that anybody was suspicious. i mean, the weird thing about somerset hospital was, is that they were planning on firing me the night before, so they let me work one more shift knowing that they were going to fire me the next day. so, they let me work an additional shift with the suspicion that i had harmed patients, which i... you know, was kind of a bizarre thing to do. >> kroft: did you harm anybody that night? >> cullen: no. >> kroft: with cullen gone and the medical center uncooperative, detectives braun and baldwin decided they needed an ally inside the hospital to help them gather evidence to make their case. they decided to approach amy ridgway, a critical care nurse who worked with cullen on the night shift and was his best friend at the hospital. >> ridgway: he was always early, always on time, crisp, and sat down and was very serious about getting to work. >> kroft: did you consider him to be a good nurse? >> ridgway: i did.

>> kroft: when the detectives first interviewed ridgway, she was hostile and upset that cullen had been fired, so they decided to show her the evidence they had gathered-- the pyxis records showing cullen's drug withdrawals from the dispensary and his real employment history. what did you tell her, do you remember? >> baldwin: i just told her that he was released from several facilities. there were allegations about him at other facilities for doing similar things that that were going on at somerset medical center. i guess, at that point, she realized it couldn't be a coincidence. >> kroft: and she offered to help? >> baldwin: yes. >> ridgway: danny pushed this piece of paper across the table to me, and it was the pyxis printouts. and i was devastated. i knew. i knew he was murdering people. >> kroft: how did you know that? >> ridgway: there were so many withdrawals of lethal medications.

there's no reason, no reason except, if you want to kill someone. >> kroft: were you angry? >> ridgway: i was sad for my patients. i was... so many things were going through my mind. i was sad i didn't see it. i felt betrayed by my own intuition. >> kroft: amy ridgway, who later persuaded cullen to do the interview with us, spent days analyzing medical records for the detectives and schooled them on a computerized record system that would help reconstruct cullen's activities on specific days. she recorded phone conversations with cullen and wore a wire at a meeting in this restaurant the same day a newspaper article reported that he was being investigated for killing patients. >> ridgway: i said, "i know you're guilty, i know you did this, and yet i'm still here. i'll take you down to the station.

we'll go together." and he changed. his face just changed. >> kroft: and what did he say? >> ridgway: he said, "i want to go down fighting. i want to go down fighting." >> kroft: cullen told us he suspected that the police were listening in. >> cullen: i knew that amy had helped the police. i strongly suspected that she was wired when she was asking me those questions. so, you know, that didn't stop me having the same opinion of amy, which is that she's a good nurse, that she's a caring nurse, and that she did it because she felt it was the right thing to do. >> kroft: he was arrested right after that meeting on what police admit was mostly circumstantial evidence. what they needed was a confession, but cullen refused to say anything. so, once again, the police turned to amy ridgway for help.

what did you say to get him to confess? >> ridgway: i wasn't very honest with him, and there's a part of me i still feel guilty about that. i was... i was manipulating him a bit. i told him... i told him the investigators were also looking at me, and how could he think that i wasn't somehow going to be implicated? i remember saying to him, "so, who was... who was your first victim? and was it a long time ago? was it recent?" and he started to talk. he said it was a long time ago. >> cullen: i believe it was with a medication to drop the blood pressure. >> kroft: cullen's formal confession with the detectives would last seven hours.

>> graeber: we will never know how many people charlie cullen killed. >> kroft: charles graeber spent seven years investigating the case for his book, "the good nurse." >> graebar: it's very difficult going back. there is no paperwork, no bodies to exhume. he's working over 16 years. in st. barnabas alone, he later told investigators he was dosing three to four people a week. he didn't always know their outcomes. >> kroft: how many, do you think? >> graeber: i would be very surprised, as would pretty much everyone i've spoken to with any knowledge of this case, if it was not in the hundreds, multiple hundreds. >> kroft: you've been in here a while. >> cullen: nine years. >> kroft: you knew it was wrong? >> cullen: yes, i did. >> kroft: at the time? >> cullen: at the time and later. >> kroft: are you sorry, what you did? >> cullen: yes, but, like i said, i don't know if i would've stopped.

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>> stahl: not since the dinosaurs disappeared have animals been going extinct as fast as they are now. entire species vanish every year. and while our hearts are moved by the plight of the biggest-- whales or elephants; the fiercest-- tigers, even sharks; and certainly the cutest, like pandas, what about the slowest? the turtle, and its land-loving cousin the tortoise, have been plodding along, slow and steady, for more than 200 million years.