A criminal who testified against one of the killers who escaped from a high-security New York jail has spoken of his fears of being targeted.

Lee Bates, 38, was sentenced to 15 years to life after pleading guilty to second-degree murder in the death of businessman William Rickerson in December 1997.

He told a court in Lockport, New York, that he had driven from North Tonawanda, Buffalo, to Ohio as Richard Matt, 48, tortured his former boss and then eventually killed him during a more than 24-hour ordeal.

In a phone interview with CNN, he said: "You've got a dangerous criminal and sometimes you don't know if you're safe, what his next move is and it's like reliving a nightmare over and over again just seeing him on TV.

"If you wanted to take a picture of the devil, that's the face that you would choose.

"He used duct tape to tie Mr Rickerson up, he beat him with anything and everything that he possibly can - a knife sharpener, a security device at the club for my automobile, he physically grabbed Mr Rickerson's hands and pulled his fingers back until they snapped, punching him, beating him.

"In a fit of rage he reached into the car, grabbed Mr Rickerson by his head and snapped his neck in front of me."

Bates gave evidence against Matt during his trial in 2008.

The court heard that Matt had been fired by Mr Rickerson days before he was killed and that during the ordeal he repeatedly demanded money from his former boss.

After breaking his neck, Matt dismembered Mr Rickerson with a hacksaw and then dumped his remains in the Niagara River. He then fled to Mexico, where he killed an American during a bar fight.

Gabe DiBernardo, a retired police chief in North Tonawanda, said he was uneasy after learning Matt had escaped.

He told the Buffalo News: "It's not a good feeling to know he's out there. Anything is possible with Rick Matt.

"I keep watching the news, and I hope they stop him before he does something violent again, because he is full of violence. That's his life."

Matt and fellow convicted murderer David Sweat, 34, used power tools to cut their way out of Clinton Correctional Facility in New York sometime on Friday night.

The men sliced through a steel wall, crawled down a catwalk, broke through a brick wall, cut their way into and out of a steam pipe and then sliced through a chain and lock on a manhole cover while making their escape.

A major search is underway in the town of Willsboro after a potential sighting of the two fugitives.

It was the third time Matt had attempted to break out of prison, including one previous successful attempt.

In 1986, he escaped from New York's Erie County Correctional Facility after scaling a fence and gate topped with razor wire. He went on the run for five days before he was recaptured at a family apartment in Tonawanda, his son Nicholas Harris told the Buffalo News.

Sweat was serving a life sentence for the murder of a sheriff's deputy in 2002.

A female prison worker has been questioned in connection with the escape.