Serial killers are 'very complicated psychologically, to investigate,' experts say

As the search continues for a person of interest in a string of homicides in Stockton, that police believe are connected, criminal justice experts are giving insight into how law enforcement agencies investigate these sorts of crimes."By definition, you could probably very well call this serial killing," Stockton police chief Stanley McFadden said in a press conference.Still, McFadden said it was not known whether one or more people were responsible for the five shootings that are believed to follow the same pattern. To learn more about these types of crimes, KCRA 3 spoke with Annie Deets, director of trial advocacy and an assistant professor of law at the University of the Pacific McGeorge School of Law.Deets, who is not affiliated with the investigation in Stockton and who spoke with KCRA 3 about these crimes in general, said investigating serial killers is "very complicated psychologically."Below are questions and answers from an interview KCRA 3 conducted on Monday with Deets.Q: How does a law enforcement agency know when it has a serial killer on its hands?Deets: "Sometimes it's related to characteristics having to do with the victims, so it could be victims of a certain gender or age range. And then it really goes into things having to do with the modus operandi, right, so how are the crimes being committed? Do they involve a similar MO? Are similar weapons being used? Are they being committed in a similar manner at a similar time of day, at similar types of locations? Is there a kind of a signature that is being left that is the killer kind of leaving -- what we think of as a calling card? Are they leaving something behind at the scene in a similar way? Are the killings being committed in a similar manner? So if it's a crime involving a gun, is the shooting being done in a similar part of the body? Things like that.Also with serial killers, there's usually not a motive that you would think of as, a motive that traditional kinds of murders have. So, most murders are driven by what we think of as kind of common things as love or money, or revenge -- those kinds of things. But serial killers really are motivated by kind of complicated psychological factors. So, really, investigators are looking for clues or more complicated things that are these common characteristics that are tying crimes that are really not related, because the victims in each case don't know each other. So, what are these kinds of small clues that tie these killings of unrelated people together in a way that we can start to draw these clues together and figure out who is doing these things?"Q: It seems like just because you have more victims, it doesn't necessarily make it easier to solve a case.Deets: "In a lot of ways, it's infinitely more complicated. Serial killers are kind of notorious for being geographically mobile. So, they will not only flee from city to city but state to state. So, just because you have a kind of a cluster of killings in one geographic region, they may have come from a different state or a different city. So, it's really important that law enforcement from different cities in different states are quickly reporting the characteristics of these crimes to one another so that they can be searching databases for similar crimes and different cities and different states to see if there are any clues that can be derived from those other law enforcement agencies."Q: What sort of questions do investigators ask the families of victims as they are trying to piece all of the clues together?Deets: "What the victims were doing, and what had changed in their lives? Maybe, if there were any new people who had entered the lives of their family members, recently, if there was anything unusual going on if there were any disruptions in typical patterns in our lives if there had been any unusual communications if there had been any new kind of people that they'd been interacting with online or in text messages, or if they joined some new club or gym, or if they had suddenly reported that they were disturbed by somebody who had been contacting them, or, did they have a new love interest, or was there a new friend, or was there something different kind of what had been happening in their lives in the recent weeks or months, kind of leading up to this -- anything that had been unusual. And also just trying to figure out where they had been, where they had been in the days leading up to the loss of their life, and what can they figure out from the small clues sometimes. They always say the devil is in the details and in these types of killings, I think that is more true than in what we would think of, as you know, unfortunately, what we call kind of more typical killings."Q: When does law enforcement know it has a serial killer on its hands?Deets: "I think that's a hard question to answer. I think what they're doing is, they're sharing information. That's why it's so important, pivotal, that they're sharing information as they get it. As they share information, they say, you know, look, we've had now three killings within kind of this month period of time, or these two months period of time, and they share these four characteristics, right, and they haven't been solved, and they don't follow what we think of as traditional patterns, right?There hasn't been any real motive that we can think of. There haven't been any real suspects that we can think of. There hasn't been any defining characteristic for any of these three or four murders, right? We can't think of anything else. And they seem to share these distinct characteristics. And once you find that they all kind of have a common nucleus of characteristics, I think that's when they can safely say, this seems right. This seems like a serial killing. It's three or more killings that share a common series of characteristics that seem to be committed by a common actor or again, it could be actors. It's just that that's how it's kind of defined in the code."Related CoverageStockton serial killings: Everything we know and don't know so far Video of person of interest released, ballistics connect shootingsHow the Stockton community is coming together amid serial killing fearsStockton serial killings: Everything we know and don't know so far