new carefree ultra protection liners, with wings! absorb ten times more, like a pad but feel thin and comfy, like a liner. new carefree® ultra protection™ tonight on "nightline," anatomy of an arrest. inside the frantic 48 hours leading to the arrest of raymond clark. the yale lab technician police say strangled ivy league bride to be annie le. closing in on a killer, surveillance footage, security swipe cards, nearly 300 pieces of evidence and the suspect's dna sample. tonight, how police broke this case wide open. and an innocent man condemned? a house fire leaves three little girls dead and their father sentenced to die for their murders. but now modern science reveals deep flaws in the conviction. was this man wrongly executed?

it's a "nightline" investigation. captions paid for by abc, inc. tonight on "nightline," anatomy of an arrest. inside the frantic 48 hours leading to the arrest of raymond clark. the yale lab technician police say strangled ivy league bride to be annie le. closing in on a killer, surveillance footage, security swipe cards, nly 300 pieces good evening, i'm terry moran. we begin tonight with the big break in the investigation of the murder of yale graduate student and bride to be annie le. the arrest of lab technician raymond clark early this morning. it came after a frenzy of evidence collection including the dna sample from clark. prosecutors believe this killing was not the tragic result of a love affair gone wrong as was suggested but a deadly example of workplace violence. and tonight, if suspect will -- the suspect will spend his first night in a maximum security facility, a long way from where his day began as david muir reports. >> unmarked cars had surrounded this motel 8 in cromwell,

connecticut. fbi agents, local police all gathered here, waiting for word from new haven's police chief. they knew the arrest warrant was coming for raymond clark, iii who worked in the same building where annie le did her research. he was inside a motel room here with his father. authorities got the green light shortly after 8:00 this morning. barricades went on the highway in front of the hotel and fbi agents raced up the back stairs straight to room 214. there they found raymond clark in a white shirt, tan pants and soon he was wearing handcuffs. hidden behind tinted windows he was brought into the new haven police department. >> going to jail. >> a few minutes ago raymond j. clark iii was arrested at motel in cromwell, connecticut. >> then two hours after his arrest, -- >> this is number 15, raymond clark.

>> he was arraigned in court. in the murder of annie le. when asked if his rights had been read to him, he said clearly yes. abc news has learned authorities have been closely following clark for days. the surveillance began not long after annie le's body was discovered hidden behind a wall panel at the yale building last weekend. a team of investigators watched as the lab technician went on with his everyday routine, reportedly playing softball, going to a fair and visiting his parent's house. first quietly following him and then the surveillance was more overt as clark became the primary person of interest. authorities had been pouring over the images from the surveillance cameras in the research building and had begun to sift through nearly 300 pieces of evidence. among the most crucial we're told are the access cards used to get into the building and from room to room once inside. the hartford currant is reporting after entering the building the day she disappeared, annie le passed through the basement and then swiped her way into a separate

lab room. her card was never used again. it's now believed clark swiped his way into the room too. it might have been the last person to see annie le alive. abc has learned that clark was in and out of the building ten times or more in the hours surrounding the disappearance, in rooms he never would have entered. dr. henry lee served as state police commissioner in connecticut, and now he helped to advise the forensics teamworking this case in recent days and says that the access cards have provided a time line inside the lab building on the last day that annie le was seen alive, revealing any opportunities a suspect would have had to harm annie le. what could the swipe cards tell us? >> they tell us that they have a means or opportunity. >> there are reports that the cards -- the swipe cards put them both in the last room where she was. >> that's become very crucial information. >> and sources tell us there were also e-mails or text

messages between clark and le. that clark at one point claimed about the condition of the mice cages in the lab, that they had been left dirty. it was his job as technician to clean them. this those message -- in those messages he suggested the two of them meet. the authorities would not say if the communication went beyond that. after days of following raymond clark, tuesday night, the detectives moved in with a warrant to obtain dna samples from his hair, his fingernails and a swab from his mouth. they tried to question him, but he invoked his rights to an attorney, offering little to investigators. then 3:00 a.m. wednesday morning they let him go. criminal experts say it's not uncommon to a let a prime suspect go after questioning. it allowing the investigation to continue at a far more rapid pace. clearly once you go into custody, all of your rights kick in. that can obviously stop certain parts of the investigation. >> and there was one more thing police were waiting for. the dna. last night, with raymond clark

clearly the prime suspect and yet still a free man, the new haven police chief said it would take one thing. >> if we have one match on a person who was at that location, we'd go for the arrest warrant. >> there were bloody surgical gloves and a bead from annie le's necklace on the floor, a sign of struggle. then dr. lee learned of the arrest. when you heard of the arrest this morning, did that say to you right away there must have been a dna match? >> yes. i know there was a match. of course, it's a relief. >> tonight, raymond clark has been moved to maximum security prison in connecticut and they believe there was only one killer in this case. annie le and raymond clark never had a romantic relationship. clark was a lab technician and they would pass each other in the hallways. today, the family of the fiance released a statement saying we want to thank all of those who

were involved in preparations for a wedding that was not to be. for their quiet understanding. annie will live in our hearts forever. i'm david muir for "nightline" in new haven, connecticut. >> and one hopes this arrest brings some brief respite for those families continuing grief. our thanks to david muir for that. we're going to take a break. when we come back, did texas execute an inknow isn't man? that is the question in the case of a father put to death for killing his three daughters in an arson fire. tonight, the compelling new evidence. welcome to progressive. how may i help you? i'm looking for a deal on car insurance. i think i might have a coupon in here. there's an easier way. we've got the "name your price" option. you do? follow me. you tell us how much you want to pay, and we'll build you a policy that fits your budget. and i still get great coverage? uh-huh. go ahead. you're the boss. i'm the boss of savings. more like the c.e.o.

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question -- do you believe in the death penalty? polls show most of you would answer in the affirmative. of the 50 states 35 allow for the execution of criminals. question -- would it change minds and laws if it could be shown an innocent person was put

to death? well, there is now compelling evidence that suggest the deadly mistake may have been made in a texas murder case. evidence marshalled in a recent investigative story in "the new yorker" magazine called trial by fire. kameron todd willingham was put to death by lethal injection by the state of texas on february 17, 2004. they said he set the fire that killed his three little daughters in corsicana, texas, two days before christmas in 1991. a fire he escaped from. >> heavy smoke damage in the room. there's heat damage. >> here, in a video taken a few days after the fire investigators walked through the house, trying to figure out what happened. >> this is the bed where the 2-year-old was found in the middle of the bed. >> they looked for clues they thought the fire left behind. and those clues they decided meant only one thing -- the fire was deliberately set and todd willingham was the man who set

it. doug fog was one of the arson investigators. you remain very confident this was arson? >> oh. >> but three conclusion is now widely concluded by scientists throughout the country to be deeply flawed. do you believe that the state of texas executed an innocent man? >> i do. i do. >> david grann is a reporter for "the new yorker" magazine. his recent story showed that the investigative techniques used to send willingham to his death have been discredited by modern science. >> this fire has been examined multiple times by separate of the leading fire investigators in the country. each one has concluded that there is absolutely no evidence of arson or that a crime ever occurred. >> last month, an official report to the texas forensic science commission, a state

panel reviewing the willingham case blasted the arson investigation as nothing more than a collection of personal beliefs that have nothing to do with science-based fire investigation. and even the original prosecutor in the trial admits the foundation of his case that arson killed those children is now undermined. you would agree that this report from the texas forensics science commission calls into serious question the methodology and the way this arson investigation -- >> without question. >> that it really has a problem? >> that the techniques used were flawed. >> deeply? >> yes. >> but john jackson strongly insists he sent a guilty man to the death chamber. >> some of the evidence is certainly less than -- less credible than i would have liked to see. >> doesn't that give you pause at all about sending a man to death? >> not a man like todd. >> a man like todd.

todd willingham was certainly a man from the wrong side of the tracks. a man with a criminal record. mostly drug offenses and a robbery. his wife stacy said todd had beaten her including when she was pregnant. to the prosecutor, that history of spousal abuse was key. >> the best evidence to me is not the investigation of the arson. the best evidence that i believe i presented was the prior attempts of todd willingham to kill his children. >> he beat his wife when she was pregnant, therefore he killed his children in the fire? >> i think that's a major factor that most finders of fact such as jurors would consider. >> todd's wife stacy specifically denied jackson's argument in the trial. and insisted her husband while violent towards her would never have hurt their children. stacy declined our request for an interview through a family member. >> we don't execute people who beat their wives. and the only question that matters in this case is did

kameron todd willingham set a fire on december 23, 1991, that burned down his house and killed his three children? >> so it comes back to the fire. doug fog and man well vasquez showed where the floor was charred, where flames were seen bursting out of the windows. where there were brown rings on the concrete porch. it all looked very suspicious. >> i have no doubt that the fire was deliberately set. >> what's the best evidence for that? >> the elimination of the causes. we found the liquid accelerant. >> that's right. lab tests showed the presence of a flammable liquid on the porch near where the family kept a barbecue grill and lighter fluid. but all other tests throughout the home showed nothing suspicious. nevertheless, fog decided todd willingham had lit a fire at the

front door and the fire had followed a trail of liquid accelerant through the hall and into the children's bedroom, where they were sleeping. and where the floor was badly charred in what the investigators determined were pour patterns. >> i am very convinced of what i saw, what i did, and that i didn't make mistakes. >> all these indicators are simply based on folklore. they're old wive's tales. >> since the willingham fire in 1919 there has been a -- 1991, there's been a revolution in the analysis and understanding of fires. gerald hurst is one of the pioneers of that revolution and one of the many leading fire analysts who have looked at the willingham case. this is a typical fire? >> a typical fire. >> he was executed for arson for the murder of his daughters. >> that's right, he was. because the people who investigated the fire did not understand the behavior of fire.

>> the fire investigators in this case were convinced they had evidence of arson. the floor was suspiciously charred. >> this led them to believe that kameron todd willingham had poured an accelerant, some type of gasoline or charcoal lighter on the fluid and it burned from the areas which reflects the patterns. >> that's what arson investigators used to believe, but no more. since the willingham fire, scientists have performed rigorous tests like this one in oakland to explore what really happens in fires. when the heat builds up in a room, when it reaches a certain temperature everything just ignites and the floor burns. >> hot gases bank down and that radiation is enough to igniter inning materials and base boards and not only ignites them but accelerates the burning. >> and scientists know that the

tell tale signs of arson in the willingham case and many others, those pour patterns of floor charring for instance, they all occur naturally in fires. >> the proof that they used for arson in here is in the report and in the testimony and that is not proof. so, yeah, willingham was innocent. he was innocent, if for no other reason because nobody ever showed any form of proof that this was an arson. >> but to doug fog the original fire investigator, the science does not matter. >> they're going to take it to these labs and they're going to disapprove it. well, i'll take it to the lab and disapprove it, but come to the real world some time and don't let the beast get ahold of it. >> was it an accidental fire or was it as prosecutors say a killing driven by devil worship, when we come back.

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so you can record in one room and watch in up to six others. (cable guy) you can do that with cable! call the verizon center for customers with disabilities living room. at 800.974.6006 tty/v bedroom. at 800.974.6006 tty/v kitchen. (announcer) get the multi-room dvr from verizon fios over the past two decades there have been major advances in the science of fire investigation. advances that have discredited the arson evidence in a case that sent a young man to the death chamber for a fatal fire and toed -- and forced the prosecutor to lean on far more circumstantial evidence. inside the willingham residence, the investigators found a charred floor, proof of arson they thought, but modern science has discredited that theory. nevertheless, john jackson thought that the so-called pour

patterns on the floor proved something else too. that todd willingham worshipped satan. >> it's perhaps a pentagram kind of a figure that some people associate with devil worship, that sort of thing. >> you think that todd willingham poured accelerant in the shape of a pentagram, some kind of devil worship thing? >> i think there's very possible and very likely. >> it's likely? >> yes. ♪ >> jackson also learned that todd was a fan of the heavy metal group iron maiden and had posters and tattoos of skulls and other heavy metal imagery. based on the fact that he liked heavy metal and iron maiden and liked the metal rock groups, and had tattoos, that makes him devil worship? >> no, but it makes him more likely that he's a devil worshiper or he's obsessed with

satan-like figures, that sort of thing. >> that's evidence that he killed his children? >> that's certainly one factor that i find -- a finder of fact could consider. >> jackson offered him a plea bargain, confess to killing his children and his life would be spared and he refused, angrily. >> i think it's likely to say that a life sentence for him would be worse than a death penalty. >> isn't it also possible he just was telling the truth when he said i will never plead guilty to something i didn't do? especially killing my kids. >> i don't think it's a good possibility that willingham ever told the truth to anybody about anything. he's one of the most completely manipulative individuals you'd ever hope to find. he's still manipulating us from the grave. >> john jackson is now a senior judge in course a -- in

corsica corsicana, he stands by the case. they say it's based on primit e primitive, old wives tales, folklore. >> not to say that they're not correct though. >> you sent man to death on that. >> i'm comfortable with that. >> beyond a reasonable doubt? >> beyond a doubt. >> there was other evidence, the fact that todd escaped with only minor injuries. a jailhouse snitch, a mentality ill drug addict who's since recanted his testimony. but it really boiled down to the arson evidence. and todd willingham. >> july 26, 2001. >> reporter david grann obtained letters and diaries that willingham wrote on death row. >> i could handle being here for something that i did, but to be persecuted for nothing i shall never understand. no god who cared about his

creation would abandon the innocent. >> on february 17, 2004, todd willingham was put to death. he said just before he died, i am an innocent man convicted of a crime i did not commit. i have been persecuted for 12 years for something i did not do. from god's dust i came and to dust i will return. so the earth shall become my throne. todd willingham was 36 years old. a spokesperson for rick perry who denied clemency even after the arson evidence was undermined told us his decision was based on the totality of the issues. when we come back, tonight's "closing argument" on this topic.