I do often wonder about stories like this in the context of forensic science – my (incomplete!) understanding a lot of the time suspect DNA samples are taken from small areas and amplified significantly with high-cycle count PCR. I'd worry that any jury presented with a statistical argument about a fragment of somebody's DNA being very unlikely ("1 in 100 million") to be different to the sample found at the scene would not be aware of all of the potential systematic reasons why the actual true probability may be much, much higher.
Probability seems to be one of those things humans habitually mess-up at.
"The chances of this person's unique DNA showing up at the scene are a zillion to one!"
"What does that really mean when the sample also contains unique DNA for a hundred other people? Did all of them commit the crime as a group?"
Depends on how they're using it. To find an unknown person and prove they were at a scene - yeah you'll have the 100 person's worth of DNA to sort through and then match against a (presently) incomplete DNA database. But if you already have a suspect and need to place them at the scene, if their DNA is one of the 100 then they have shown that.
But we’re they at the scene or did they just bump into someone or something that was there?
That's something that would have to be addressed at the trial by the defense attorney raising challenges.
If the DNA is present, it's present - barring any procedural mistakes by the forensics technicians (mislabeled sample, dirty lab equipment, didn't follow manufacturers instructions, etc). Or deceit by one or more members of the forensics team to implicate the suspect.