Was looking around the internet and ran into the following:

According to NBC 5 Chicago, Mr Crimo’s identity was first made known to authorities because of the DNA collected from the rifle discovered at the scene.

Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives conducted a rapid trace of the rifle, agency spokesperson April Langwell told the Associated Press on Monday. Federal agents conduct such traces to identify when, where and to whom the gun was last sold.

NBC 5 later confirmed that this rapid tracing was how the authorities narrowed down Mr Crimo as a person of interest.

The Independent

The man was identified due to the rapid trace by the ATF, which took DNA recovered from the rifle found at the scene.

Federal agents conduct such traces to identify when, where and to whom the gun was last sold.

Tampa Free Press

Uhh, OK..?

No idea why his DNA was on record.

Any ideas?