Why DNA at a crime scene is sometimes totally meaningless

Remember that time I wrote about the SCOTUS decision on DNA swabs taken from someone who was only arrested, not convicted of any crime, and why that was a terrible, terrible ruling?  Some people responded to my hypothetical in that first post by saying it was so remote of a possibility that it was nonsense (see the comments on that for responses).

I mean, who cares what I think? I'm just some fear-mongering public defender who gets criminals off on "technicalities" (also known as "your constitutional rights"). I mean, I am clearly conjuring up the most ridiculous, far-fetched scenario possible just to freak people out. It's so unlikely that something like that would ever actually happen. 

Except for that time that is totally did. 

And not way back in the day when DNA testing and forensics were still new and mucky sometimes. Actually, it happened pretty recently. In November of 2012. 

Here's the article for the full story, but the nutshell version of it as follows:  millionaire guy is murdered in his home. They are able to extract unknown DNA from on the guy's fingernails. The assumption is that the DNA must be that of the killer. They run the DNA through a database and get a hit to a local man named Lukis Anderson. Mr. Anderson is arrested and charged w/ murder and faces the death penalty. He spends 5 months in jail, awaiting a resolution on the case.

However, it is impossible for Mr. Anderson to have been involved in the crime because on the night the man was killed, Mr. Anderson was in a hospital due to severe intoxication. He had been brought to the hospital by paramedics earlier that evening.  Airtight alibi if there ever was one. So how did his DNA get on the dead guy's fingernails? 

Well, according to the theory that the prosecutors have put forth, after finally conceding it wasn't possible that Mr. Anderson was the killer, is that the most likely explanation is that the DNA was unintentionally transferred by the paramedics.  You see, the paramedics that had taken Mr. Anderson to the hospital earlier in the evening were the same paramedics that responded to the crime scene and that handled the millionaire's body.

The only thing that saved Mr. Anderson from being tried (and probably convicted, given how everyone thinks DNA is completely infallible) was his airtight hospital record alibi. Let's all hope we have such credible, documented alibis when and if we're ever wrongfully implicated by DNA evidence in a crime we didn't commit. Otherwise, we're screwed. Even with that alibi, Mr. Anderson spent 5 months in jail for a crime he had no involvement in whatsoever before the prosecution finally conceded he couldn't have possibly been involved. 

Not concerning enough for you? Well, what about Germany's "Phantom of Heilbronn," a notorious female serial killer who linked by her DNA to 40 different crimes, and yet somehow continued to manage to evade police during her crime spree that left police baffled for 2 years? She was also linked by DNA to several cold cases. Except for the devious serial killer turned out to be an innocent woman who worked at the factory where the cotton swabs used to collect DNA evidence were made. The Phantom of Heilbronn never actually existed. 

We've all been conditioned to believe that DNA is the smoking gun of guilt, the indisputable indictment in a case.  If the defendant's DNA is found at the crime scene, then the defendant committed the crime. Case closed, end of story. 

But, it's not. DNA technology continues to advance to the point where minute amounts of DNA can be detected and a profile can be created. So, your old items that you sold at the thrift store can suddenly place you at a crime scene. Your doctor or paramedic can accidentally transfer your DNA to a crime victim. It's not as unlikely as we all want to pretend it is. 

DNA isn't the rock solid evidence we want to believe it is. But, no one will believe that until they themselves are in Mr. Anderson's position. Until then, until they are in jail for a crime they know they didn't commit, people will continue to believe that DNA = guilt.