If you want to learn more about how DNA can help find criminals (and others), you probably will want to read an article written by Brian Bouchard and published in the WAGMTV web site at: https://www.wagmtv.com/2022/06/20/how-your-dna-could-be-used-help-solve-cold-cases/.
This article is an excellent introduction to the subject although long-time DNA experts probably will find it to be a bit too basic for their use.
Bouchard describes a recent local case in which law enforcement personnel used the services of Investigative Genetic Genealogists to identify a person based upon DNA information. He writes, "...in cases like this one, the victim's DNA undergoes full genome sequencing in an attempt to find any matches against a third party database. The database is primarily made up of at home DNA test results."
He briefly mentions the controversy of privacy concerns concerning the use of public DNA databases that were not created for purposes of law enforcement. However, there are other online articles that discuss those concerns in greater depth than does this one article.
Comment by Dick Eastman: I was rather surprised and impressed to see this article published in the WAGMTV web site. Many years ago, I was employed at WAGM for several years and none of the employees ever mentioned DNA (to me) in those days. It is nice to see today's employees are keeping up with the current technology.