A Casper man is behind bars, accused of beating his pregnant girlfriend.

Twenty-Nine year old William Dyson has been charged with one count of aggravated assault and one count of interfering with a 911 call.

Prosecutors say Tuesday night (May 2nd), Dyson's girlfriend told police she had been hit once in the face by a closed fist from Dyson, after the couple got into an argument.

The blow knocked her down, and she told investigators Dyson then sat on top of her, with his knee in her abdomen.

Dyson's girlfriend is seven-months pregnant and she was concerned about the condition of her child.

While she was on the phone with 911 operators, investigators say Dyson took the phone away.

He is being held on five-thousand dollars bond, awaiting trial.