A woman who sat on her boyfriend and suffocated him to death during a drunken rage is facing nearly four decades in prison after she admitted to his murder.

Windi Thomas stabbed Keeno Butler in the hand with a knife and battered him with a table leg before she smothered him with her body at their home in Erie, Pennsylvania, prosecutors told the Central Court at the Erie County Courthouse.

The 44-year-old pleaded guilty to the third-degree murder although her lawyers argued the she killed Mr Butler by mistake after collapsing on top of him while drunk.

Mr Butler's death was ruled homicide caused by “respiratory insufficiency secondary to blunt force trauma to the neck and thoracic compression, exacerbated by blunt force trauma to the head.”

After killing the 44-year-old in March, the court heard that Thomas dialled police and told a dispatcher: "I killed my boyfriend."

After arriving at property, investigators found a table leg with bolts protruding covered with blood.

She told police that she had been drinking and looking to purchase crack cocaine.

As a result of the plea deal, her recommended sentence will be reduced from 20 to 40 years in prison to 18 to 36 years.

Defence Attorney Mark Del Duca said it was a good result based on the facts of the case.

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“Obviously, it's an unfortunate situation for everybody, but I think that this guilty plea and the recommendation we've made to the court will be beneficial for all parties involved," he told GoErie.com.

Sandra Butler, the Keeno’s sister, told the site that she wanted to see Thomas serve more time than the agreed-upon sentence.