I'm Alexis linklater. And I'm Billy Jensen. When detective Jim sharf snapped the cops on William Talbot, he knew that genetic genealogy could be a revolution in law enforcement. But he didn't anticipate what it would fully reveal. Just one month earlier, Golden State killer Joseph Deangelo had been identified using genetic genealogy. One month after talbott, it would be Raymond roe. Two of those three offenders had no serious criminal history. I started noticing that a lot of these other people that were being arrested by the use of genetic genealogy are people that only did it once or there's only DNA left at one crime scene. I'm thinking what kind of a person are we dealing with here? Our investigation of the row and Talbot cases in the previous episodes exposed an undeniable implication. Profiles can only be so useful in hunting down someone who has never killed before and then never kills again. In this final episode, we're asking the question, what is the future of profiling in light of genetic genealogy? And how can it possibly plan for this type of killer? Paul holes, who spearheaded the investigation of the Golden State killer, recognized the problem facing profilers when he heard the details of Raymond roe killing Christy marac. If I were to take a look at the crime scene, this looks like a predator, likely committed, you know, priors and possibly committed more afterwards, the characteristics are there. Therefore, this is likely a serial offender. Did profiling just not account for this species of killer. The previous models are a little bit problematic from a behavioral analysis standpoint. Now, you have the one offs who commit a similar enough crime that can fool those of us that have worked serial cases. There hasn't been a really good comprehensive study to figure out, well, what is going on with these offenders? These are professional investigators with decades of experience under their belts. And they're realizing how easily they can be fooled. Why? Because they've been taught to rely on the model that profiles have been selling for decades. When the FBI started its behavioral analysis unit in the 1970s, the focus was on serial killers. These were the headline grabbers, the real-life monsters that captured America's fear and fascination. People like Ted Bundy, Charles Manson and Dennis Rader, the BTK killer, are perfect examples. Law enforcement would call them lust murderers or something to that effect. They started to study these lust murderers, the serial offenders. There was this idea that serial killings had this sort of addictive quality. What are your thoughts on that? It became apparent that many of them had a very act of fantasy life about the violence. Prior to them ever committing the crimes. And that they would continue to fantasize, even after they had committed the crimes. So profilers in the early days felt that this fantasy was so core to the person. That that would be such an addiction to them, that they would continue to do that until they could no longer do that. You hear the phrase that serial killers never stop, and so if a series stopped, it's assumed that while they went into custody. They became disabled. They've died. The addiction theory, by definition, would not pertain to a one and done killer. But that type of offender was not being studied, or even really acknowledged. If the person wasn't caught quickly, they just weren't caught. And those crimes were then assumed to be part of a serial killer spree, yet to be identified. But even with all the attention being given to serial killers, how accurate were the conclusions..