New laws in Maryland and Montana are the first in the nation to restrict law enforcement’s use of genetic genealogy, the DNA matching technique that in 2018 identified the Golden State Killer, in an effort to ensure the genetic privacy of the accused and their relatives. Beginning on Oct. 1, investigators working on Maryland cases will need a judge’s signoff before using the method, in which a “profile” of thousands of DNA markers from a crime scene is uploaded to genealogy websites to find relatives of the culprit. The new law, sponsored by Democratic lawmakers, also dictates that the technique...