re: forensic evidence in sexual assault

Real rapists use condoms all the time nowadays. It really depends on their nature, and how much they're concerned about getting caught. If he's prolific he's going to leave some DNA behind though, whether by hairs, or skin left behind by abrasion, or a victim fighting back with fingernails. He'd have to be very careful to leave no trace of his DNA behind, perhaps if he dumps a litre or so of bleach in a bathtub full of water before dumping the body in there? That would erase everything except internal DNA, and the condom would cover that base.

Not unusual to use a condom - whether someone would more depends on their particular pathology, type and motivation than knowing they should for evidenciary reasons.

As to how much semen will help an investigation - not having a record is not that unusual, again depending on the above, and semen isn't helpful to find someone, only to eliminate someone, unless it's someone you've got that kind of evidence on already.

As for the psychic, most legit departments won't touch that kind of nonsense, the feds won't at all.

rosehips said:

ETA: I've been thinking I wanted to avoid a Dexter-esque criminal mastermind, as I tend to believe most criminals aren't like that.

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Problem is, if he's as you described him in the original post, not too bright, compulsive, and leaving DNA strewn about, with a record of his DNA on file, it's not going to be tough to figure out who he is. The only way things get tough is if he's off the grid. If he's living under an alias with a good fake ID, or he's literally off the grid, camping or squatting in an abandoned building, earning cash through under-the-table work or criminal activity. You'd figure out who he is, but DNA doesn't tell you where to find him.

Also, if you've got a psychic, why are you worried about the lack of realism in 'smart' criminals?

Studies have shown 34% or more of rapists are sexually dysfunctional, and that 40% wear condoms

*Rape Investigation Handbook (John Savino, Brent Turvey)

Semen isn't the only way to determine a person's identity. During the course of a rape investigation, a PERK (Physical Evidence Recovery Kit) is used to find hairs, clothing fibers and saliva.

*Police Procedure and Investigation (Lee Lofland)

As others have already stated, the existence/matching of DNA without an actual name linked to it would only serve to verify that the same individual committed the offenses, so the investigators still wouldn't know his identity based solely on that.

I believe rape is about power and control. A rapist who does not want to get caught and who wants to have control over the rape scene, wears a condom. He would also make sure he takes every precaution not to leave any DNA evidence (hair, blood, semen) behind, and no fingerprints. Just because he's a serial rapist/killer does not mean he's careless. In fact, the fact that this rapist leaves nothing behind could be his signature.

The thing is, one day this careful rapist/killer will screw up and make a mistake, and most likely with a victim who throws him off guard. However, since your killer odes not become careless in this story, if he doesn't leave anything behind then the police might not be able to catch him unless.....

He targets victims in a certain area. The police can watch a certain area and have the chance of spotting the killer at work. Give him an MO to where he does not kill in a neighborhood, but perhaps he targets a certain kind of woman no matter where she is in the city.

The psychic still has to have something to go on. Just because she is psychic does not mean that she will just "pick up" his vibes. Maybe she is an excellent criminal profiler and notices things that the police do not. Maybe she goes undercover to try and get this killer.

All in all, it sounds like an interesting story. Keep working on it and it will come together.

The killer might also wear a condom because he doesn't want to catch any diseases from the women he rapes. This might work especially well for your story if he believes women are "dirty" or "unclean" or believes sex is inherently dirty. For the investagators it would be the same result, even if the reason was different.

rosehips said:

Hi again,
I'm hammering out the details of my serial killer, and as I am somewhat basing him on a real perp (Sacramento's Roaming Rapist), he'll be sexually assaulting his victims before strangling them to death. So here is where I have a concern:

How likely is it that a serial rapist/murderer would have the forethought and discipline to wear a condom so as to avoid leaving semen behind?

It seems unlikely to me. So then... how realistic is it that a police force that did find semen on victims would have trouble tracking down the perpetrator? I suppose if he didn't have a criminal record... but that seems unlikely in a serial offender.

I need this guy to be so hard to catch the local law enforcement can't do it without the aid of my mc, a psychic. One of my other characters is a detective and I don't intend to portray him or his colleagues as incompetent. Rather, I'd like to create a criminal who somehow is hard to find.

I hesitated over whether to post this here or in the Sandbox as I think part of what I need is just a bit of story help, but since I also could use the expertise of those of you who can tell me how common it is for serial rapists to use condoms and how useful semen is to an investigation, I opted for this board. Thanks in advance for your help and your patience with me.

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Having some background in criminal psychology and forensics, I can tell you that many (not all) investigators view serial rapists (murders, arsonists etc.) as either organized or disorganized. These are terms coined by the FBI's Behavioral Science Unit and are not medical terms. However, they are terms used in profiling individuals who commit crimes.

Disorganized offenders tend to be of lower intelligence/education, have more run-ins with the law, poor personal hygiene, don't tend to give a lot of thought to the crime they are committing and take few precautions. The organized offender tends to be of middle to higher intelligence, having completed high school/possibly college, good personal hygiene, careful selection of targets, may watch the news to follow the police investigation and plan accordingly.

As I said, not everyone subscribes to profiling. If you use this method, I would suggest that your rapist is organized. Otherwise, the police would have to be pretty incompetent not to find any number of pieces of physical evidence a perpetrator can leave behind. Semen is only one of many. Of course, if he has no prior record or military service, then prints and DNA samples are only useful if they catch him. Contrary to your comment, many serial killers/rapists do not have prior criminal records. This is why they can be difficult to catch.

Finger prints, DNA and bodily fluids are of little use in determining his identity if they have nothing to match it too. Other physical evidence can often be more helpful, such as a partial sole print from a shoe that has a limited market. You can narrow down what store carried it, how many were sold and possibly too which customers. This was the case for the serial killer, Richard Ramirez, the Nightstalker.

Hope this helps.
Joe