St. Paul, MN (KROC-AM News) - A Duluth man has been sentenced to 30-years in prison for killing his girlfriend’s young son.

24-year-old Sterling Anderson was prosecuted in federal court because the crime occurred on the White Earth Indian Reservation in northern Minnesota.

The U.S. Attorney for Minnesota says Anderson pleaded guilty last November to a second degree murder charge for assaulting the 3-year-old boy in October 2015. The severe beating left the child with traumatic external and internal injuries, which resulted in his death within a matter of hours.

Anderson initially claimed the boy fell and struck his head while running in the nearby woods, but later confessed and told investigators he had become frustrated by the child’s crying.