Serial killer Michael McGray has been charged with a sixth murder: the 1985 killing of Nova Scotia teenager Elizabeth Gail Tucker.

Police forces across the country have reopened old cases ever since McGray was caught in Moncton last year. He says he's been involved in up to 16 murders across Canada.

McGray, 35, was arrested in Moncton after slitting a woman's throat. That's when his history as a serial killer came out.

Michael McGray

In media interviews from prison he told reporters he'd killed 16 people, including the Dartmouth teenager back in 1985.

McGray has offered to plead guilty to this and other murders if the police would meet certain conditions. He wants better treatment in jail and he wants immunity for anyone who was with him during those murders.

RCMP Sgt. Wayne Noonan says the police aren't making any deals. "About a year ago ... he laid out some conditions for a guilty plea. But none of those conditions were met by the RCMP," said Noonan.

Elizabeth Gail Tucker

In spite of the confession, police needed more evidence in the Darmouth murder before they could charge McGray. Now they have it.

"This file was never closed. This person McGray came to our attention several years ago and it's just through very exhaustive investigation that we found the corroborating evidence that he's admitting to," Noonan told reporters.

Noonan says he can't say if anyone else will be charged in the Tucker murder. And he says the police won't talk about any other investigations involving McGray.