of course, rather than a mental illness. It is possible that a stalker has a major mental illness, but stalking is a behavior that generally fits into the Cluster B personality disorders, which are characterized by thinking and behaviors.
In the Idaho case, the suspect's thinking included a fascination with mass and serial killers. In his studies at college, he came up with the now infamous survey for criminals to describe in detail their thinking and behaviors before, during, and after they committed their crimes. His top professor was Katherine Ramsland, the internationally known criminologist who studied mass and serial murderers. Her best known work was on the BTK killer.
Predatory stalking is not limited to identifying one victim, most obviously in cases where a person is looking to kill more than one person. Now, a mass murderer often plans to die at the scene of their crime -- think of most school/ public shooters -- although they may experience second thoughts. Still, a significant number don't even wait for police, and kill themselves. This is where some of the key dynamics associated with predatory stalking are important. Like the other public shootings, the killer has identified a "soft target." I will suggest that a house of all female residents is generally a softer target than a house full of males. And there is more.
A predator looks for a safe exit from their attack. There is a huge distinction between stalkers who want their victims to know they are being stalked, and those who are fully intent upon not being identified. An obvious example is the BTK killer, who had done surveillance to identify victims he believed to be soft targets, and was familiar with the locations in a manner that allowed him to both strike and exit without notice. That applies to the Idaho killer as well, as the late hours that he was in that neighborhood previously shows -- as does the number of times he circled around the house in the hour or so before the murders.
I agree that he was attempting to commit the "perfect crime." In fact, I'll take it a step further, and say he wanted to commit the perfect crime, that would shock the nation, and remain a mystery. Killing one person doesn't fit that bill. Picking a random house that he is unfamiliar with -- who resides there, and likely the lay-out -- does not fit at all.
Finally, before I ramble on too long here, you are correct that a stalker usually picks one victim. In the first three types I mentioned in the OP, that is almost always the case. The only exception that comes to mind is when an unstable person has an unhealthy belief that, say, the house they grew up in actually "belongs" to them, not the people that bought it. This is an example where both a house and person/people may be the target.
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