> up next, a vibrant real estate professional is brutally murdered. >> this involved the entire range of violence. >> even hardened professionals are troubled by what they see. >> for there to be that much blood left at a scene, that's what we consider overkill. >> police find a possible witness and try hypnosis to get every detail. >> how many times do you see a composite sketch and you're like, this looks like every human being on the face of the planet? >> it was a real whodunit. and i hate whodunits. >> the killer leaves behind a clue, but will it be enough? >> people will kill for the most trivial of reasons. on a hot summer day, a married couple decided to look at a sample home in a ranch housing development in mckinney, texas. when they walked into the sample home, they couldn't find the sales associate. but they knew right away that something was wrong. >> and they walked into the

living room, and then they saw a blood trail leading into the kitchen. >> and that's where they found the sales associate, sarah walker, in a pool of blood. >> the victim was stabbed 27 times. there was an incredible struggle. >> furniture and plants were knocked over. it looked like the victim fought for her life. >> it just didn't happen in a little two by four square area. if you can picture a bar room brawl, that's probably what was happening in that show house. >> for there to be that much blood left at a scene, that's what we consider overkill. >> sarah walker was 40 years old, recently divorced, and the mother of two children. >> when i answered the phone, it was the mckinney police department. he said sarah has been assaulted and as a result has died of her injuries. and i just started screaming. >> sarah worked for a real estate company showing model homes to potential buyers and

was very successful. she also appeared in some sales videos. >> we're so proud to be in a neighborhood like this. it stands out above all the rest. >> she was thrilling and she was exciting and full of energy. she would walk into a room and she would just light up the place. she had enough energy for, you know, four or five people >> police found a bank surveillance video recorded a few hours before sarah's murder showing her making a deposit. in the video, she was wearing an expensive ring and watch. neither one was found on sarah's body. >> the watch wasn't at her home when he searched her home. it wasn't in her car or at her office. so we started to think pretty soon, whoever had killed her, had taken that ring and a that watch. she had it on two hours before she died. that helps us prove, in fact, a robbery occurred. >> police also discovered that

the killer most likely posed as a client. >> she was talking to my cousin. she said, i'm sorry, i have to go. which means there's a customer here, i'm going to go sell a house. >> just 30 minutes later, sarah was dead. it was hard for investigators to imagine a crime of this magnitude in an upscale housing development. >> things just didn't match, really. it just struck me as the last place i would expect a crime like this to occur. >> we had a real whodunit on our hands if it was a random attack. we were very concerned that someone who would kill sarah in this manner was somebody who would probably not hesitate to do this again. >> with a killer free, no one, especially mckinney police, could sleep easily. honestly? this deal was way too good to believe. instead of paying too much for an ipad,

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as investigators analyzed the scene of sarah walker's murder, they quickly discovered that she was killed in the living room after a horrific struggle. it was also clear that the killer was injured too. >> he turned the dead bolt knob and he closed the blinds, but his hand was already cut. so he left his blood in both of those places. and then at some point, he dragged sarah into the kitchen and then he tried to clean up, because that was his blood in the sink. >> investigators also found perfectly round drops of blood on the floor of the kitchen near the body. >> that shape is indicative of blood being dripped straight

down from a 90-degree angle, straight down. >> the blood evidence provided police with the killer's dna profile. at the autopsy, the medical examiner discovered no sign of sexual assault. but he did find something extremely unusual. apparently, during the struggle, the killer bit the victim on the neck. >> it almost brought this crime down to the level of savagery. i'm looking at the evidence of one animal biting this woman because she's some sort of prey for him, that he's going to take and do with what he wants to. >> in a search for suspects, investigators first looked into sarah's personal life. they discovered that sarah had recently been divorced from her second husband, randy tate. >> there was no love lost between the walker family and randy tate, let's put it that way. >> randy tate was the last known person to see sarah alive.

sarah dropped their son off at his house earlier that morning before she went to work. >> bottom line is i want them to catch whoever did this. >> according to family and friends, it was a divorce she did not want. she was not happy about it, she was hurt by it. so we knew there were some tough feelings. >> randy tate claimed he had an alibi, that he was playing golf with friends at the time of the murder. >> he was initially very cooperative, but later became hesitant when it came to dna. and seemed to be very angry. >> but tate did provide his dna, and it did not match the blood dna at the crime scene. next, investigators checked an internet dating site that sarah joined called millionairematch.com. sarah didn't date many men since her divorce, but when your photograph is on an internet dating site profile, there is

always the risk of danger. >> think about it this way. if i exchange one e-mail with a random stranger or if i just write something like no, thanks, i'm not interested. you have a suspect right there. if you return 30 or 40 no thank yous in a week, and trust me, women get inundated with that many questions. well, you've got 40 suspects. >> investigators interviewed all the men sarah spoke to from the site. each provided a dna sample and all were eliminated. by this time, several weeks had passed. and the trail of sarah's killer was turning cold. then unexpectedly, nelson villavicenzio, the husband of another realtor, came forward with some new information. he said on the morning of sarah's murder, his wife got a call from a man who identified himself as chan lee. he wanted to see the model home located across the street from

the home where sarah was killed. >> she felt a little suspicious about him and wondered if he was legitimate. and she tried to call the hotel he said he was at to find out what time he was coming, and he was not in the room that he said he was in. >> in fact, no chan lee was registered at the hotel, but she still agreed to meet him. >> remember when you're in the real estate business, you're in the business of making a commission. so you're going to accept all comers. >> the realtor did take precautions. >> my wife asked me if i wanted to come along, and i said yes, and i did it for my reasons. >> when they arrived, an asian male drove up in a white mustang. >> he had a t-shirt, no sleeves, jeans, sneakers, very athletic. and i asked him, excuse me, sir, is your name chan lee, and he looked up in the sky. did not make any eye contact with me and sort of gave me a vague loose saying like no, but

he didn't express anything. >> the man walked quickly to his car and drove away. while nelson and his wife waited in the townhome, they saw sarah walker arrive for work across the street. >> i yelled at my wife, come and check this out. there's a beautiful blonde coming out of this sports car and she's going to the model. my wife said oh, that is sarah. and i said, oh, sarah is looking very good. she said, well, yeah. >> when nelson and his wife realized that their appointment was a no-show, they left, and saw the white mustang parked next to sarah walker's car. nelson said they considered stopping by to say hello to sarah. >> said well, are we going to go visit with sarah? and my wife said no, we're hungry, so we left. >> they left at approximately 1:00 p.m. sarah's body was discovered 20 minutes later.

>> the possibility of we had visited sarah and found myself and ourselves in the middle of it, of something terrible, will always be on my mind. >> i consider nelson's wife to be very lucky. i think there's a high likelihood she would have been the victim that day had she not brought her husband along with her to that subdivision. >> police now had a possible eye witness. but would it be enough?

real estate sales woman sarah walker was robbed and murdered in the sample home of an upscale neighborhood housing development. her friends and family reacted with disbelief. >> the family has suffered beyond imagination. >> i believe she deemed it to be safe. she was very, very excited about the community when she was first placed over there. my fondest memory of sarah, she would laugh at all of my jokes whether they were funny or whether they were stupid. she would still just laugh, so that always made you feel good. >> in a fortunate turn of events, a witness came forward telling police he might have seen sarah's killer.

unfortunately, by the time he came forward, several weeks had passed and police feared he might have forgotten some of the man's physical characteristics. >> nelson had such a brief look at this person, i was hopeful but also doubtful that it was going to work. >> so police decided to try forensic hypnosis before asking nelson any questions about the man's description. >> the purpose of forensic hypnosis is to bring out the detailed memory from the subconscious. >> nelson was sent to richard shing, a texas ranger and a trained forensic hypnotist. >> you get them relaxed and then in that relaxed state, you bring up a date or an offense and place them in the incident where they may recall an incident. >> it has been used since the 1800s. in texas they've reported a 75% success rate.

>> under hypnosis, the images in your mind, the remembrances become so clear that i've got lot of faith in his hypnosis. >> the memory is already there in his mind. the memory, i'm not placing a memory in his mind. it's already there. we're just actually going back and revisiting that day and time. >> the hypnotist wanted nelson to think of the incident as if he were watching a movie. and then freeze frame the image of the man he saw at the model home. nelson described the suspect as asian, muscular, around 27 years old, 5'7" tall with a buzz hair cut. after he described each feature, he then looked through a book of photographs to choose the most similar. >> every one -- if you look closely, they have different shaped eyes, mouths and noses, and that book gives the witness an opportunity to flip through

the pages and pick out different features that the suspect had. >> slowly, an image emerged of the man nelson saw that day. >> i was saying that with these facts and the sketch, we'll hit jackpot. >> the composite drawing kind of brought the case back to the front burner again, because for awhile, we had nothing. >> the sketch was released to the media and immediately produced results. yet another local real estate agent said she recognized the man. she rented a home to him. and she said once he came to her home asking to use her phone. when she refused to let him inside, he grew angry. >> he was banging on her back door, and now she's terrified. her dog's going crazy, this guy is now in her back yard banging on they are back door, so then she calls the police. >> police identified the man as

25-year-old kosoul chanthakoummane, his parents were from laos, but he was born in the u.s. a background check indicated he drove a white mustang, worked as a delivery truck driver, and had a history of violence. >> from age 15 forward, he was in jail. he assaulted a classmate, severe enough to be sent to juvenile detention. when he was 15, he was out on that offense for several months, and then stole a car. >> after that, he robbed and kidnapped two elderly women in north carolina. he was released on parole just six months before sarah walker's murder. >> he was paroled to texas because his sister lived here. and his sister was willing to help him try to get his life back on course. >> when he was interrogated by police, kosoul denied any involvement in sarah walker's murder. >> i don't know what you're doing, man.

i don't know i didn't do anything. >> we're trying to find out the truth. >> i think you know. >> what truth, man? >> you washed your hands, went over there and got a drink of water? >> his left hand looked like he had been in a fight. >> the scars weren't lined up all along the same plane. they were kind of going every which way. >> and police had a secret weapon. the bite mark on sarah's body. would it match kosoul's teeth? ef business. when possibilities become reality. with centurylink as your trusted partner, our visionary cloud infrastructure and global broadband network free you to focus on what matters. with custom communications solutions and responsive, dedicated support, we constantly evolve to meet your needs.

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thanks to an eyewitness and forensic hypnosis, investigators now had a suspect in the murder of sarah walker. 25-year-old kosoul chanthakoummane. although he denied any involvement, prosecutors were convinced that he was the killer. >> kosoul was a psychopath and a sociopath. by that i mean, no matter where he is, he's always thinking about himself first. all about him. what can he get for himself and do for himself? and others? others are to be used for his pleasure and his needs. >> since the perpetrator bit the victim, sarah walker, investigators took photographs

of kosoul's teeth and made dental impressions. the impressions were then compared to images of the bite mark. >> what we tried to do is we tried to make it not match. we tried to rotate the models. we tried to flip them around. we tried to make it not work. and it just kept going right back to perfect match. it was as positive as i have ever been about doing a forensic dentistry case. >> ironically, evidence found on kosoul's cell phone indicated he had a fascination with biting. >> he'd been fantasizing about this. he had a photograph on his cell phone of him pretending to bite his own dog. >> finally, his dna profile matched the dna of the blood found on the floor next to sarah's body. prosecutors believe kosoul preyed on female real estate

agents because they often worked alone. on that tragic day in mckinney, texas, the evidence shows that kosoul called his first target, asking her to meet him at the model home. but she sensed trouble and brought her husband, which frightened him away. >> excuse me, sir. are you chan lee? >> but kosoul didn't give up. he saw there was another model home across the street, and he saw sarah walker arrive for work. >> oh, you know what? somebody just walked in. won't be able to stay on the phone. >> prosecutors believe he went inside and tried to rob sarah. >> give me that watch. >> there was a fight. while trying to subdue her, kosoul bit her, then he used his knife and stabbed her more than 20 times and cut himself in the

process. nelson villavicenzio and his wife were just outside while the murder occurred. had they stopped in to say hello to sarah, they, too, might have been victims. in october of 2006, kosoul was convicted of capital murder, and sentenced to death. >> people will kill for the most trivial of reasons. reasons that no rational person would ever imagine. >> what the science did in this case is it made that defense attorney get up in his opening sentence and say my client was guilty and this was a robbery gone bad. he would not have said that if we hadn't had the physical evidence we had in this case. >> this case turned out to be the perfect marriage of good police work, excellent science, and prosecutorial expertise.

it was the perfect blend of all three of those things coming together, to where we got the case from the day sarah was murdered until he was convicted and sentenced. and sentenced. >> up next, a wealthy businessman is killed by an intruder. >> there's blood everywhere. >> can you tell where he was shot? >> no. >> investigators find a wide-ranging conspiracy. >> the murder had been planned out. >> other people not only knew about it, but had been asked to participate. >> friends turn on friends. >> i didn't do anything. >> it didn't seem to be sinking in with him how deep he was involved. >> but to get the killer, one piece of evidence had to be identified. >> all these high school kids had been involved, and perhaps one of them did it. just after midnight in st. cloud, minnesota, 17-year-old