A US man allegedly filmed himself having sex with his step daughter's corpse moments after shooting her in the head.

Prosecutors say video confirms that Gregory R Graf, 53, murdered Jessica Padgett last month so he could have sex with her body, Philly.com reports.

Authorities claim Graf, from Allen Township, Philadelphia, told officers that he was driven by desire when he allegedly shot 33-year-old Ms Padgett in the back of the head on November 21.

Graf is also suspected of hiding Ms Padgett's body on his property, where he allegedly ran a marijuana-growing operation, while family and friends frantically searched for her.

Northampton County District Attorney John Morganelli declined to detail the contents of the video, but reportedly confirmed it showed Graf committing a variety of sexual acts on the corpse.

Mr Morganelli said he had allowed an "abuse-of-corpse" charge to be filed against Graf.

However, as Ms Padgett was deceased at the time of the alleged sexual abuse, he cannot pursue the death penalty.

Desecration of a corpse is not an aggravating factor in Pennsylvania, as opposed to sexual assault while a victim is alive.