Why would a forensic DNA test take so long?

On TV and the movies, DNA tests are damn near instantaneous- at most, a few days. A bit of research shows that, in reality, two to four weeks is standard, with some results within days.

The reason I ask is because of this story, about Susan and Jerry McFalls. Basically, the two of them disappeared from their rural house in southern Utah- their house was left open, with food still on the table, and with no signs of violence or foul play. I’ve been following this from the beginning- my friend is the couple’s niece.

Several months later, with almost no leads at all in the case, two bodies were found in a ditch not too far away. Susan’s body was identified almost immediately thanks to a registered hip implant. The other body, though, has not yet been identified… and it’s been almost 240 days at this point. The investigators haven’t released anything about the cause of death, and have no real timeline on when they expect to be able to identify the second body and give the family some closure, if not answers.

I can imagine the bodies were in pretty poor shape after being out in the desert that long, but surely some DNA would be intact. I realize that, thanks to the movies, we expect DNA tests to be the silver bullet that closes cases, but this seems just… weird.

The most likely explanation is the huge nationwide backlog of forensic DNA samples.

As for other possible factors - there would be no problem getting a sample from the body, but they don’t say what it’s being compared to. It sounds like there’s a son. It’s possible that they have tested and it’s a case of non-paternity, and they can’t talk about that.

DNA has this in common with fingerprints and dental records. Unless you have a match between your sample and some identifiable individual (in the case of DNA a near relative will do) you cannot make a positive ID.

Dental records are often mentioned in older detective stories, but unless they know which dentist the corpse used and they actually had some identifiable work done, it just wouldn’t work. You kind of get the impression of all the dentists riffling through their filing cabinets looking for a match.

I would have thought that there would be plenty of matches in the house though, to at least confirm that he lived there, so delays in the system are the more likely cause.

The theme from the article was “we just get so many more samples now, we can’t keep up.” The numbers went from 242,000 submitted samples in 2011 to 308,000 in 2017. Um, so like a 27% increase over 6 years? That doesn’t sound like crazy exponential growth that just can’t be kept up with…unless there is lack of funding (or mismanagement).

So it sounds like it is just not a priority to the people controlling the money.

The tests can be done in a day or two, and most of that time just requires cheap automatic equipment, not human action. Anything longer than that is due entirely to backlog, and the backlog is probably due entirely to lack of funding leading to not enough labs. They probably didn’t have enough labs in 2011, either, so there was already a backlog building up.

And while all you can do is to compare to specific individuals, in practice, that’s not usually a big deal, because conventional police work has usually narrowed the field to a very small number of likely prospects. Like, here, there’s no guarantee that the male corpse is the husband, but that’s still the way to bet, and in the very likely case where they test against him and come up positive, they don’t need to test anyone else.

Cadaver ID is probably not prioritized over active homicide, sexual assault, etc. cases, either.

The article says that the body was sent to the FBI lab. That is not usual if all they have to do is match DNA. If I wanted to get a DNA match all I would have to do is get a tissue sample from the county coroner and whatever known sample I had and send it to the state lab. The fact that the entire remains were sent to the FBI suggests it’s more complicated than a simple DNA match.

Recall the notorious case of Paul Bernardo in Toronto in the 1990’s. He raped a number of women in Scarborough and was identified as one suspect. His DNA was taken, but over year later the materials had still not been tested, when he’d moved to St. Catharines, where he and Carla Homolka, his wife, kidnapped, raped, murdered, and dismembered two teenage girls. One claim was that if they had tested faster, those girls would be alive.

Apparently that’s been an ongoing problem across North America; I think it was Chicago or Detroit where thousands of old rape kits had never gotten around to being tested.

And yes, most ID’s of random individuals require reference sample - a certified relative or sample that undoubtedly came from the same person. If, for example, a son’s DNA does not match - there may be a simple explanation for that. Keep in mind too, a sibling or other relative match is not definite unless there is no doubt this is the only missing relative.

I’m pretty sure the backlog of thousands of rape kits is a thing in most major cities in the US.

Surely they could also have compared it to DNA from the couple’s home, from his toothbrush/hairbrush etc.

I suppose there is also a possibility that the body is not that of Jerry and he is on the run for double murder…