DNA match in cold-case killing likely, says expert

Police say Mallory Manning slaying is among the most brutal they have seen. Photo / APN

The odds are high that police will find a match for unidentified DNA on murdered prostitute Mallory Manning if it is that of the killer, a crime expert says.

Ms Manning's family are also backing police to find the person they are looking for almost three years after she was bashed and stabbed, and her body dumped in Christchurch's Avon River.

Police described the killing in December, 2008, as among the most brutal they had come across. It appeared she was taken to a section occupied by the Mongrel Mob and attacked there.

Police revealed yesterday that Ms Manning, 27, was also sexually assaulted, and a semen sample had been recovered from her body. The semen would have been left at the time of her death or very close to it.

From this, a full DNA profile was obtained within days of the killing. In the time since, police have compared the DNA profile against hundreds of people, including Ms Manning's partner at the time and two clients Ms Manning had on the night she was killed.

None of these comparisons provided a match.

Criminologist Greg Newbold said if the man who left the semen on Ms Manning's body was the killer, his criminal inclinations meant he would have the "sword of Damocles" hanging over him.

"Because it only takes one incident where police are able to take DNA and they are able to identify the person by the computer [DNA database]," Mr Newbold said.

If the person who left the semen on Ms Manning's body was a client of hers who never broke the law, then finding a match would be much less likely.

Detective Inspector Greg Williams denied police were going public now because they had drawn a blank.

"In every investigation like this, we always consider what [information] we retain and what we release. At this point, we have determined it is time to release it."

Ms Manning's brother, Robin Manning, said he was happy with the police progress.

"We have got full faith in what they are doing. I'm fully 100 per cent confident they will find the person.

"I really think it's just a matter of time ... and there will be some slip-up made.

"The fact that the person is still roaming free, and has the potential to do this to someone else ... I guess that's the most discomforting factor of them all."

Mr Williams said police believed more than one person was involved in Ms Manning's death.

People could come forward or nominate others.

"A lot more people now are going on to the [DNA] databank, and I think it will only be a matter of time anyway."