Terry Davies was the father of Ryan Davies, who was kidnapped, raped, and murdered.
History
When the prime suspect was identified as Bill Turbit, a registered sex offender, Terry shot him to death outside a courthouse after an initial civil commitment hearing to determine whether Turbit should be sent to a mental institution. Terry immediately surrendered to the detectives for his crimes. It later turns out Ryan's real killers, were two teenage boys named Jimmy G. and Mike D., were later arrested.
Terry was executed for Bill's murder. (SVU: "Uncivilized")