Here's what to look for in an investigation: Is there anything missing that belongs to the victim? Often police will mistakenly look for valuable missing items. But I'm not talking about a stereo component -- that's an impersonal item. I'm talking about something more personal -- a ring, earrings, even costume jewelry -- something the victim was wearing at the time of the crime.

Maybe they'll keep the victim's driver's license. Some will leave it intact. Others will get rid of everything but the picture, so they just have a little wallet photo of the victim, as if they had some kind of relationship going.

In the more sadistic cases, some killers will take locks of the victim's hair, or even go so far as to cut off the head or other body parts.

Reliving the crime

Between crimes -- often while targeting future victims -- they'll pull out their trophies and just sit back in their La-Z Boy chairs and relive the crime over and over in their minds.

What's interesting is that they often give the souvenir -- particularly jewelry -- to a family member or significant other. The recipient could be the wife or a girlfriend who was causing the subject grief at the time of the crime or was involved in a confrontation with him.

Well, the subject goes out and commits the crime, and like the cat who catches the mouse, brings it back and drops it on the doorstep. He'll present his wife or mother with a piece of jewelry and say, "Look, I found this on the street. I want to give it to you." When he sees this person who is a part of his life wearing the item, it becomes part of a game. He looks at it and fantasizes about the victim he raped or murdered, and it's like his own little secret: "If only she knew ... what she's wearing right now came from one of my victims."

His way of thinking is that the wife or girlfriend somehow caused him to go out and rape or kill.

'Removed garbage from society'

Though they may say they committed the crime, they never really accept responsibility. They'll blame it on someone else, or their upbringing, or say they were abused as kids. Or it was the victim's fault -- "She was wearing a short skirt, John. She wasn't even wearing a bra. She was looking for it. She's promiscuous. What did I do? I removed garbage from society."

They'll never say, "Gee, I'm so sorry for what I've done here." The tears may well up in their eyes, but -- and I've always said this -- they're crying for themselves. They could care less about the victim.

Sometimes they'll BS you into thinking they believe it's all their fault, but they're only going along with the program so they can get out of jail.

Not all killers take trophies. David Berkowitz, the Son of Sam, didn't take any tokens because his crimes were very impersonal -- he was shooting from a distance. But he did go to the gravesites of the victims. He went there not because he had any remorse, but to symbolically roll in the dirt because, for him, this was an accomplishment. Again, see, it's all fantasy.

Sense of 'ownership'

When they finally commit a crime, it's like they have a sense of ownership. It's an accomplishment and they feel so good about what they've done that they have to keep it going, like some athlete in his 40s who's always pulling out an old scrapbook.

Many of us get trophies for our accomplishments. For killers, taking souvenirs extends the fantasy into that realm. My accomplishment may be solving a case. I get a plaque or some kudos; their accomplishment is perpetrating a crime. I get to put the plaque up on the wall of my den. They get to take something from the victim to give to the girlfriend, or put up in the attic.

It's surprising how many killers return not just to the gravesite but to the scene of the crime. And some killers -- the more organized or premeditated type -- sometimes even inject themselves into the police investigation to provide bogus information. They do it for different reasons. They may want to find out where the investigation is headed or look for cues that it's progressing along nicely because, naturally, they're concerned about that.

They may go to the police in order to beat them to the punch, just in case someone may have seen them or provided a description of their car. This way, if their names pop up later, they can come back and say, "Oh, wait a minute, I went to you guys a month ago. I was cooperative."

Follow press coverage closely

They'll follow the case very closely and keep newspaper clips of their crimes. This is helpful to the investigator -- something you want to look for when you initiate a search warrant.

Assassins are notorious for keeping news clips. Assassin-type personalities will also keep diaries. The disorganized type of criminal -- that's the asocial type, the loners, the weird -- will keep diaries because they have trouble communicating with others so they feel much more comfortable writing out their thoughts, plans, goals or fantasies. Sirhan Sirhan, who gunned down Sen. Robert F. Kennedy, and Arthur Bremer, the would-be assassin who shot and paralyzed Alabama's then-Gov. George Wallace, kept diaries describing the fantasies they wanted to act out.

It's like in the Wild West, where they used to cut notches in a gun. The whole thing seems like it's relived. It's fantasy, but it never ends. It doesn't even end when you incarcerate the killers.