A South Dakota man has changed his plea to guilty in a Morton County gross sexual imposition case.

Nikolaus W. Black Elk, 27 of Manderson, S.D., pleaded not guilty in June to the Class AAfelony, but changed his plea to guilty Thursday at the Burleigh County Courthouse.

According to court documents, Black Elk was charged for having sex with a 13-year-old girl in January 2005.

An affidavit from Mandan Police Detective Dave Shipman said the girl went to the doctor on June 9, 2005, complaining of cramps and back pains. It was learned at that time that she was about 41/2 months pregnant, the affidavit said.

The girl told authorities that she had been sleeping at Black Elk's home, and he came in, removed both of their clothes and had sex with her sometime in January 2005, court documents said.

Black Elk provided police with a DNA sample after the June hearing. According to court documents, the DNA test identified Black Elk as the father of the baby.

Black Elk was originally slated to stand trial Wednesday. Instead, he changed his plea to guilty Thursday.

Black Elk faces up to life in prison and must register as a sex offender. A presentence investigation will be held to help determine his sentence. A date has not been set yet for his sentencing hearing.

- Jenny Michael