Say there’s someone you hate, and they screwed you over in some fashion. To get back at them, you take a steaming dump on their deck. Can that poop be traced back to you by investigations?
That’s the crappiest idea I ever heard.
Did this person steal your million dollar “sell a bunch of weeds” idea? I bet it’s a pretty nice deck.
<insert “poop deck” joke here>
DNA evidence.
But is there enough for a forensics lab to actually extract meaningfully? Has there been an actual legal case that was proven by identifying fecal matter with a specific individual and where the court accepted that evidence?
This wasn’t in the US, but yes…
Yes, there would definitely be DNA in feces.
I suppose your victim might pay for the testing and might get a court order for a DNA sample that would allow them to match you to it.
Yeah, there would be plenty. You don’t need very much using amplification techniques. Fecal matter contains remnants of sloughed off cells from the digestive tract and other material that contains your DNA. Analysis of DNA in fecal material is now a fairly standard technique in wildlife biology.
In fact, it’s so mundane as to be use to catch pet owners who don’t pick up after their dogs: Dog DNA Scooping Owners Who Fail to Pick Up After Pets - ABC News
I think Paris officials were the first to use it in this manner. Now there are kits to be used by Landlords and Neighborhood associations.
Of course there is enough DNA there. There is a ton of DNA in feces. The main problem is that there are a lot of PCR inhibitors as well. But these are easily taken care of with the correct extraction protocol.
The “court order” you’re describing is a search warrant, and there are specific rules for obtaining one - the most notable of which is the requirement for probably cause, meaning they can’t get DNA directly from you without your consent unless they there is some other evidence that suggests you may be the guilty party. Moreover, the warrant would be issued to the police, not to the victim - and I would bet the police have better things to do than to put that much effort into ID’ing a deck dumper.
Just visit some dog parks. Bring a gallon sized zip lock bag. Keep the collections moist. Collect a lot.
Better yet, got any cow pastures nearby? 
If I’m in a civil action, I can’t subpoena a DNA sample from the opposing party? I thought the standards for subpoenas in civil court were much lower than in criminal matters. If there’s evidence of an ongoing dispute (e.g. broken contract negotiations) and a party sues for deck damages, it seems reasonable that a judge would grant the subpoena. But I don’t practice civil law–anyone?
On the technical side of things, how does a lab discriminate between bacterial and fly DNA from human during the extraction and cataloguing process? Do they get reports on all the DNA contained in a sample and look for human markers?
Usually, any test you’ll be doing on the DNA will involve some sort of PCR-based amplification steps. All you need to do is make sure the primers you use are specific to human sequences. Easy enough to do.
Could be confounded by cannibals though.
I would assume there’d be a shitload of DNA in fecal matter.
Or at least enough for a wombat to sniff out.
In his book “Bodies and Crimes: A Pathologist Speaks” F.D.M. Hocking wrote of a case where he identified a burglar from his poo, and that was before DNA was invented (Ok discovered!) Its a while since i read the book but i think it was something to do with Diatoms?..though i maybe mistaken, but he did it.
(its an interesting book written by a country Pathologist (cornwall in the 50’s 60’s and 70’s)and all his odd cases, poo detection and goat bestiality included, all mixed in with very odd right wing rants. )
Perhaps the OP should watch this current video of a waiting to poop event in Canada …