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 pret