Jack Black was terrified he would be murdered when he visited a high security prison.

The actor portrays the title character in his new movie Bernie. It's based on the true story of a man who befriends an elderly woman who is rich, then kills her.

Before the cameras started rolling Jack decided to meet the man he was playing but was terrified by the trip to jail.

"It was scary," he told E! Online. "It was intimidatingYeah, we're safe because there are guards around, but you don't feel safe. You feel like you can get killed any minute."

Shirley MacLaine portrays the elderly victim Marjorie Nugent, while Matthew McConaughey is the prosecutor on the case.

In real life, the trial was relocated as legal professionals feared Bernie would never be found guilty as he had so many friends in his Texas hometown.

He was eventually sentenced to 15 years inside, which Jack thinks is fair.

"I definitely feel like he served his time," he said. "He deserved punishment, to do hard time because it was murder - but not all murders are created equal. Bernie is just the sweetest, softest and most lovable guy. It's like you shouldn't be here with these killers."

Jack enjoyed shooting Bernie and has hinted he isn't quite ready to let the character go. He has discussed making the story into a musical with Shirley.

"I'd love to do some Broadway," he said. "But it's not going to be done next week. We got a lot of work to do."