Hundreds of local men have been spoken to since the 15-year-old disappeared while walking her dog on New Year's Eve 1998, including her ex-Royal Navy sailor father Sid and older brother John, who were once considered main suspects.
Now, after eight years on the sprawling cold case file, Detective Inspector Greg Murton of Canterbury CIB has developed a "stranger-type abduction" theory involving a loner killer who lived locally, who either smoked or grew cannabis, and knew the rugged Rakaia Gorge area where Bentley's body was found 18 days after she went missing.
"That's obviously just a scenario but one that makes sense to me," he said.
Murton is convinced the initial scene at Ashburton River - where Bentley's dog Abby was found tied to a tree and her underwear and boxer shorts in a nearby bush – was staged by the killer to throw police off his scent.
"We often find in any inquiry like this, a big whodunnit where there is a massive amount of work done initially, that the offender will have been spoken to by police and there is nothing to prove or disprove their involvement at the time. There is a chance that has happened," Murton said.
He cites the brutal 1995 slaying of young Christchurch mum Angela Blackmoore, where her murderer Jeremy Powell was spoken to early on in the homicide probe, but wouldn't be arrested for another 24 years – and just months after police offered a $100,000 reward.
It was also the case for Jarrod Allan Mangels. After a drunken Nelson night out in 2003, Mangels was asked to give a blood sample. His DNA was later found to match the DNA found on nail clippings from Maureen McKinnel who was strangled at her Arrowtown home on Boxing Day 1987 and dumped naked over the Arrow River Bridge. He'd been spoken to early on the police probe but was allowed to go free.
"There are endless numbers of these, where the person has been spoken to but there's nothing to directly point towards them as being the offender and it can't be taken any further at the time, and then something later comes up that proves they are involved," Murton said.
Top international criminal profiler, retired British police inspector Chuck Burton has reviewed the Operation Kirsty file and agrees with the "stranger-type abduction" scenario, carried out by someone local.
It all but rules out anyone from the Bentley family being involved. Father and brother vehemently denied any involvement, with Sid doing so right up to his death in June 2015, aged 64.
"Obviously, the family were looked at quite closely – John and Sid, particularly in light of the change of story by Sid a year and a half after the murder – but I'm pretty comfortable that Sid and John were not involved," Murton said.
"I can never say 100 per cent that is the case, but my view is that it's far more likely a stranger-type abduction in that case."
The $100,000 reward for "material information or evidence" that finally brings about a prosecution – nobody has ever been charged - has already had the police phones ringing.
He hopes the reward offer, where immunity from prosecution may be considered for any accomplice - not the main offender – flushes out key information. Someone knows the truth, he said.
"It's a significant amount of money for anyone," Murton said.
"Someone might have some information that they have been sitting on and they either don't believe it's true or they are too scared to come forward.
"But relationships change, circumstances change, people get older and more mature, and they think they'll pass it on for what it's worth, and then bingo, it turns out to be the bit we needed. That's what we're hoping for."
She welcomed the reward news, saying it was "great" but didn't want to comment further.
Four years ago, Peachey who now lives in Invercargill with second husband Noel Peachey, told the Herald she didn't have any theories on what happened to her daughter. And having no answers or any clues was been one of the toughest things to handle.
"But I think of the happy memories, not the day she died. I've been through very black years of grieving and don't wish to return to that. If Kirsty's name is mentioned I smile. She is the Kirsty I remember."
-By Kurt Bayer
