His DNA must have been on file already.
DNA, with no matching records is difficult.
But a relative who has DNA on file would be a close match, so you could narrow the suspects down, which has been done................
Most states do have a DNA database of all convicted felons, and have been collecting that database for the past 10-15 years or so. The databases have solved a number of cold cases. In Indiana, the database hit constitutes probable cause to get a search warrant for a forensic sample and test. The database is not set up to be a full forensic sample.
As I said, the DNA itself does not “lie.” But the circumstances of collecting the forensic sample and establishing how it got there are critical.
At some point in the not-so-distant future, the government will be seeking DNA samples for a national database for all live births. The ethical issues and implications are many.
It was a familial DNA check of some kind. This is not telling the whole story. It could be that DNA lead to another DNA test.