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SUNRISE (CBSMiami) – A Sunrise man accused of murdering his girlfriend and then mutilating her body changed his plea to guilty on Thursday.

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Fidel Lopez, 26, will be spending the rest of his life behind bars for the murder of 31-year-old Maria Nemeth.

Investigators said Lopez admitted to becoming a “monster” when Nemeth called him by her ex-husband’s name during sex back in September 2015.

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In a series of police interrogation videos released to CBS4 News, Lopez is heard talking to police about what happened that night.

“She changed my name,” he said. “She called me the name of the other (expletive) guy. And she said it twice and she was wrong and she was confusing me with him. At that point, I get mad. I get really, really mad.”

Police said he went on to admit he disemboweled her.

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The deal ensures Lopez will not get the death penalty.