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Police have been hunting Ivan Andrew Campbell, 47, since he absconded from the Salisbury St Foundation with fellow resident Jaydon Galland, 18, on Wednesday morning.
Campbell was jailed for 14 years in 2001 for the horrific attack the year before.
He was paroled to live at the Salisbury St Foundation in June after serving 11 years of his sentence.
Police said both Campbell and Galland were high-risk offenders and, while they posed no specific threat, they should not be approached.
Campbell pleaded guilty in 2001 to a raft of charges including kidnap, assault, assault with a weapon and sexual violation.
The court heard he plied his 14-year-old victim with alcohol before holding him captive in shackles and chains in a wardrobe.
Over the course of seven days, Campbell subjected the boy to sex acts and abuse which included tattooing, piercing, branding, beatings and scalding with hot wax.
The boy managed to call for help while Campbell was out of the house.
Campbell was convicted of a similar assault on a 13-year-old boy in 1991.
Police prosecuting the case described him as a "calculating, manipulative sexual deviant" who preyed on teenage boys from single-parent homes.
Galland, a regular defendant in the Greymouth District Court, was convicted and sentenced two months ago to intensive supervision and electronic monitoring at the Salisbury Foundation.
Judge Chris Somerville said at the time that Galland needed to be kept on a tight programme to keep him occupied while receiving treatment for drug and alcohol issues.
Noting that he had a long history of violence and troublemaking, the judge said he was giving him one last chance to turn his life around.
"This is going to be quite a nice time for you," the judge said, "So make the most of it and don't cock up."
Galland had appeared on charges of unlawfully taking a motor vehicle, careless driving, wilful damage, threatening behaviour and speech, graffiti, assaulting police, procurement and possession of cannabis, and possession of cannabis utensils.
Detective Senior Sergeant Tony Hill said two sightings of Campbell and Galland had been reported in and around the greater Christchurch area overnight.
Police were following up the sightings and were keeping an open mind on the mens' possible location and movements.
The men were known to have connections in Christchurch as well as in Ashburton and the West Coast.
Police described Campbell as a 1.7m tall Caucasian of medium-thin build with extensive tattoos on his face, neck and arms.
Galland is a Caucasian of about the same height and medium build.
- By Matthew Backhouse of APNZ and Tui Bromley of the Greymouth Star