A senior detective quizzed the Ashburton Work and Income killer over one of New Zealand's most notorious cold case murders at Auckland Prison last week, the Herald understands.
Tully, now aged 52, flatted opposite the Bentley family's South St home in Ashburton for around three years in the early 1990s.
He was not identified or spoken to during the massive original investigation.
But Tully told police last week that he was married and living in Nelson, working full-time, when 15-year-old Bentley disappeared on December 31, 1998, while walking the family dog on the Ashburton riverbank.
The New Zealand Herald has learned that Tully left for Australia with his wife on February 12, 1999 – less than a month after the schoolgirl's badly decomposed body was found in the Rakaia Gorge, more than 40km away from where she was last seen.
During his police interview Tully, who was notoriously disruptive and uncooperative during his High Court murder trial, is believed to have given a detailed account of his old car, how he used to camp near Bentley's abduction site, the reasons for his Australia move, and his knowledge of the Bentley family.
Detective Inspector Greg Murton of Canterbury CIB, who took charge of the cold case in 2014, refused to comment when approached by the Herald.
It's believed that Tully, who is serving life imprisonment with a minimum non-parole period of 27 years for the Winz slayings, was one of three suspects police have been looking at closely.
The Herald revealed last year that Tully was a person of interest in the Bentley case.
Several senior detectives have handled the inquiry over the years. But to this day, it remains an open homicide investigation.
More than 300 persons of interest have been looked at, including Kirsty's father Sid Bentley, who denied any involvement in her disappearance or murder until he died of cancer in 2015, aged 64.
Murton confirmed last March that Tully, who escaped after the shootings along the same stretch of Ashburton riverbank where Bentley went missing, was being scrutinised.
"There's probably 20 or 30 reasons why someone could be of interest to us in relation to the case, either being there or previous history, or connections, and there are lots of people in that category," Murton said at the time.
"And until they are eliminated, and sometimes that's impossible, then they remain a person of interest, without being a suspect, so to speak."
Justice Cameron Mander described the shootings as "cold-blooded executions" by a "very dangerous person" capable of extremely violent actions.
Tully has lodged appeals against his conviction and sentence. A Court of Appeal spokeswoman this week confirmed no hearing date has yet been set.
Retired Detective Senior Sergeant Lance Corcoran, who led the original Ashburton CIB investigation, didn't recall Tully being either a suspect or person of interest.
"I was aware of Mr Tully before he did what he did. It's possible that he came up after my time," said Corcoran, who compulsorily retired at the age of 55 less than a year after Bentley's death.
"We never had a list of suspects, as such. Where it's a whodunnit investigation, they are all persons of interest to me. You try and eliminate them, although some remain on that list to this day."
The investigation will remain open "until it is completed, one way or another", Murton says.
