During the inquiry, a DNA profile from Ms Manning's body was attributed to an unidentified person, referred to as "Male B". Police say DNA samples were taken from a large number of people, including members of the Mongrel Mob, but they still haven't found a match.
Mr Williams believes "Male B" is probably closely associated to the Aotearoa Mongrel Mob or wider Mongrel Mob. Part of the problem investigators had was that most of the key players were gangsters or sex workers - people who talk to police reluctantly or not at all.
"We started this investigation with no identified crime scene, limited forensic evidence and efforts by some of those involved to destroy some evidence that might link them to this murder," said Mr Williams. "It has been a painstaking process over five years to gather evidence and build a picture of what occurred." But he said people from all walks of life, including those with gang connections, were shocked by Ms Manning's extraordinarily violent death.
"There is no support among the gang community for the people who did this."
Sequence of events
Prosecution case: Mauha Huataki Fawcett took part in, or was party to, Mellory Manning's slaying to earn his gang patch.
Members of the Mongrel Mob's Aotearoa chapter picked up Miss Manning from Christchurch's red light district on December 18, 2008, as part of a hit over a drug debt.
They drove her to the Mob's pad at Galbraith Ave and - to the soundtrack of loud music - raped her, beat her and stabbed her with various weapons.
Once she was dead, they stood around her mutilated body, shouted "sieg heil" and barked like dogs. Mobsters, including Fawcett, dumped her in the nearby Avon River where her semi-naked body was discovered by a kayaker the next day.
Fearing the gang would dob him in to police or kill him over fears he would grass, Fawcett fled the city. During a series of police interviews, he incriminated himself in the killing, but later backtracked.
Defence case: Fawcett conducted his own defence during the four-week trial with assistance from an amicus curiae - a friend of the court - lawyer Craig Ruane.
He claimed to have lied throughout the interviews and said police pressured and "coached" him into making false confessions.
He said he hadn't been at the gang pad that night and denied having anything to do with Miss Manning's murder.
Timeline:
*December 18, 2008: Christchurch sex worker Ngatai "Mellory" Manning is raped, bashed, and stabbed in a frenzied fatal attack.
*December 19, 2008: Her badly mutilated body is found by a kayaker in the Avon River.
*December 2010: Extremely rare mutated grass pollen found on her clothing is matched to samples from Mongrel Mob's Galbraith Ave gang pad, police reveal.
*September 2011: Police announce that semen found on Miss Manning's body did not match any of her clients that night.
*March 29, 2012: Unemployed ex-mobster Mauha Huatahi Fawcett is arrested and charged with her murder.
*February 10, 2014: Fawcett's murder trial begins in High Court at Christchurch
*March 11, 2014: Jury delivers unanimous guilty verdict.