KEY POINTS:
Police are offering a $50,000 reward in a bid to gain new information about a "highly unusual" murder of a woman in 2005.
A half naked body was found partially wrapped in a red tarpaulin, yellow raincoat and a black plastic bag in the Waikowhai reserve, Hillsborough, July 2005.
Detective Senior Sergeant Gerry Whitley said he was still confident the killer or killers of Ms Jefferies could be found.
He told reporters he was convinced a group of young men who had been drinking with Ms Jefferies before her disappearance were not telling the full truth about their knowledge of her.
Mr Whitley said he was convinced somebody knew how Ms Jefferies died and said they now had "50,000 reasons" to come forward.
Immunity from prosecution will be considered for any accomplice to her murder - not the principal offender - who first gives such evidence or information.
"The investigation team is determined to solve the mystery around Katrina's murder and today's announcement is just one more step towards achieving that aim," Mr Whitley said.
"I sincerely believe there are more than a few people in the neighbourhood where Katrina lived on Whitmore Rd, who know something about what happened to her on the night of Monday July 11, 2005. We'd love to hear from all or some of them so that we can progress this investigation for Katrina's sake as well as her son's and mother's."
Police said at the time that Katrina Ann Jefferies received injuries to the top half of her body but did not reveal how the 22-year-old mother was killed.
They described the murder at the time as "highly unusual".
Today they said the reward would be paid for the identification of a suspect leading to a conviction for the murder.
Ms Jefferies' mother was the last to see her leave the flat on her way to meet friends.
A framed print depicting a river and mountain scene, and a tatty piece of plywood, were also found with her body. It is not known if the print and the wood were put there by the killer or dumped independently.
She had upper body injuries and police said although they knew what caused her death they would not release details.
The body was not discovered until the next day.
She was not involved in drug deals and had a lot of friends and a good social life, police said at the time.
The operation number is 0800 924 569 and has been active for the past two years and will be manned again this week in the hope vital information about Katrina's brutal death will be forthcoming.
- NZ HERALD STAFF, NZPA
