The boyfriend of murdered teenager Jane Furlong has refused to speak to police since her body was found, but the officer in charge of the investigation hopes a $50,000 reward will "loosen" others who hold important information.
Ms Furlong's mother has criticised those staying silent, calling them "self-preserving cowards".
The17-year-old mother and part-time sex worker disappeared from Karangahape Rd in May 1993. Her boyfriend, Danny Norsworthy, reported her missing two days later.
Her remains were found at Sunset Beach, Port Waikato, in May last year.
Despite a major police investigation spanning almost 20 years, an arrest is yet to be made.
Mr Benefield said people involved in court cases Ms Furlong had been due to testify in for the prosecution were also refusing to speak to police. The cases involved gang members accused of an assault and businessman Stephen Collie, charged with brutal attacks on sex workers.
Mr Collie yesterday said police had not contacted him. "I've got nothing to say to them. I was in remand prison when Jane Furlong went missing."