A man who murdered his victim with a Samurai-style sword is missing from Magilligan Prison.
Stephen Henry, 41, did not return to the prison on Monday, after he was issued a day-release pass to visit his family.
Henry was jailed for murdering father-of-two John Cooke in Lisburn in 2004.
Sentencing him two years later, a judge said Henry had "behaved like a savage", attacking Mr Cooke as he "begged for his life".
On Tuesday, PSNI Detective Sergeant McColgan said: "We believe that Stephen Henry, who was jailed for murder in 2004, is dangerous and may be in either the Craigavon or Belfast area.
"He is described as being 5ft 10 in height, of medium build, with short brown hair. He has tattoos on both upper arms and scars on his forehead and left ear. "
Police said Henry was last seen in Craigavon at about 15:45 GMT on Monday.
"He has a history of violence and I would urge the public not to approach him but to contact police immediately," said Det McColgan.
He urged Henry to hand himself in to the authorities without further delay.