A man has been found guilty of killing his wife's twin sister in Massachusetts while his wife was in the hospital getting ready to deliver their second child.

A Worcester jury on Thursday convicted 24-year-old Steven West of first-degree murder by extreme atrocity or cruelty in the death of 20-year-old Alyssa Haden.

Prosecutors say West sexually assaulted and killed Haden on Oct. 10, 2012, while his wife was in the hospital to deliver their second child. The couple shared a Spencer apartment with their infant son and Haden.

West had told authorities that Haden died accidentally during sex. An autopsy determined that Haden died from asphyxiation caused by compression of her face, neck and chest.

He is facing life in prison without parole when he's sentenced Friday.