A gruesome surprise for an Alamo Square woman yesterday — human remains unearthed in her planter box — poses something of a forensic puzzle today: How do police begin an investigation when there’s not yet enough information to determine if a crime was committed?
Granted, human bones don’t usually appear in the yard through a series of legal events. But stranger things have happened, albeit few recently. (SFPD spokesperson Grace Gatpandan admits she can’t remember the last time something like this came up.)
Police will confirm only that the recovered bones are human. Previous reports identified the first remains as the jawbone and teeth of a child (more apparently turned up later), but SFPD says that only the medical examiner can confirm that, while a clerk in the medical examiner’s office says they can’t confirm that statement because it was made by the police. So we’re going to have to just stick a pin in that for now.
[jump] Imagine you’re a cop and you’ve initially got nothing to work with except a single bone. You don’t even necessarily know where it came from, because, as Gatpandan points out, the dirt in the Alamo Square planter box might have been moved from elsewhere.
So, one bone is the only clue to potentially identify a victim, a perpetrator, and whether a crime transpired in the first place. This is the sort of thing that might make even the most dedicated public servant consider knocking off early for the holidays.
But don’t despair, because science may come to the rescue.
“The first thing lab technicians are going to do is examine the bone fragment for nuclear DNA,” says Dr. Cassandra Calloway, coordinator for the forensic science graduate program at UC Davis.
(She’s also an “assistant scientist” at Oakland’s Children’s Hospital. Calloway is not involved with the San Francisco medical examiner’s investigation and commented only on the general forensic methods used in such cases.)
Nuclear DNA is the jackpot for putting a name to remains. Every cell in a human body contains thousands of strands of DNA, but almost all of it is what’s called mitochondrial DNA, which you inherit from your mother.
mDNA furnishes a lot of useful information (Calloway’s research developed many of the tools and methods modern forensics uses to analyze mitochondrial DNA, in fact), but it’s not the best way to ID someone because it’s identical to your mother’s mitochondrial DNA, and in fact to the mitochondrial DNA of all of your maternal relatives.
“If I get a matching mDNA profile, I can’t be sure whether it’s you, your sibling, your mother, your aunt,” etc., says Calloway. Imagine the luckless cop who ends up with an mDNA match for a family with multiple missing persons who then has to explain, “Well, we’ve identified someone or another, that’s for sure…”
Nuclear DNA, on the other hand, has genetic contributions from both parents and is therefore much more specific. But there are only two copies of it in any cell. Lab techs have to hope that the remains aren’t so far degraded that the precious nuclear DNA has lost all of its markers (lab shorthand for the specific parts of the genetic code that analysts concentrate on — there are about 300 billion to choose from).
With some luck you‘ll find them, and then, bingo, you’ve got a DNA profile. Now what the hell do you do with it? DNA is only useful if you have something to compare it to.
Investigators then turn to California’s missing person’s database. If this person was reported missing, and if family members contributed genetic samples for future identification, the match will be in that database somewhere, and a computer algorithm can return it fairly quickly.
If a match comes up the police department can start figuring out what’s what: They’ll know who this person is, how long they’ve been missing, who their family members are, and the circumstances around their disappearance. They’ll have all the evidence of the previous missing person’s investigation, and finally know the questions to ask to determine if this might be a murder.
And if there’s no match?
Then you file this one away in the unidentified person’s database and hope that some day the other half of the puzzle falls into the system. It’s a big cosmic lottery that nobody wants to be entered into in the first place.
The San Francisco medical examiner’s office would say only that they’re still analyzing the recovered remains. SFPD declined to comment until the analysis is complete. We’ll update you when that happens.