Kirsty Bentley killing: Russell John Tully linked to murder

A new twist in the cold case 1998 murder of Ashburton schoolgirl Kirsty Bentley has been revealed.

Double murderer Russell John Tully - who is serving life imprisonment for killing two people at an Ashburton Work and Income office in 2014 - is now being linked to Kirsty's murder, NZME reports.

But Kirsty's mother says she's not holding her breath that the case will be solved.

"Tully being on the list of persons of interest doesn't mean a lot unless there was good reason to be," Jill Peachey told Fairfax on Wednesday.

"I didn't know of Tully until the Winz shootings but I encourage continued interest," she said.

More than 300 people were considered persons of interest in the case, including Kirsty's father Sid, who died of cancer in 2015. Kirsty's brother John also was considered a person of interest. Both the men denied any involvement.

"I don't believe either Sid or John were connected in any way," Ms Peachey told Fairfax.

"They say 'never say never' and it would be great for Kirsty's killer to be brought to justice," she said.  

The lead investigator of the Bentley case, Detective Inspector Greg Burton, has confirmed Tully is a person of interest.

There could be many reasons for someone to be classed a person of interest in an inquiry, including their previous history and connections, he said.

Kirsty was 15-years-old when she disappeared on December 31, 1998, while walking the family dog on the Ashburton riverbank.

The dog was found tied to a tree near the river the next day, and Kirsty's underwear was nearby. Her body was discovered two weeks later in the Rakaia Gorge, 40km away.

Tully is has lodged an appeal against his conviction and sentence for the Winz murders.

kirsty bentley john tully murder ashburton
Kirsty Bentley

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