Abel Avila was arrested Tuesday after officers found him hiding out in San Jose, where he had been living under a fictitious identity.
Avila is accused of shooting and killing his sister's boyfriend, Arnulfo Medina, in Los Angeles on July 10, 1985.
Medina was allegedly having an affair with one of Avila's married relatives. Investigators said Avila confronted Medina on the street, pulled out a gun and shot him.
Avila has been transported back to Los Angeles and booked for murder.
