A Christian missionary from Oklahoma who claimed he was possessed by a demon has been sentenced to 40 years in prison after being convicted of sexually abusing children at a Kenyan orphanage.

Last June a federal jury found 20-year-old Matthew Durham guilty on seven counts of engaging in illicit sexual conduct in foreign places. Durham committed his crimes while he was volunteering as a missionary in Kenya’s Upendo Children’s Home near Nairobi between April and June of 2014.

U.S. District Judge David L. Russell sentenced Durham to 40 years in a federal prison Monday. He also ordered Durham to pay restitution of $15,863.

At sentencing Judge Russell called Durham a serial rapist and a child’s “worst nightmare,” noting:

These were heinous crimes committed on the most vulnerable victims. He was their worst nightmare come true.

Durham, 21, had faced up to 30 years on each of four counts of engaging in illicit sexual conduct in foreign places.

At the time of his trial Durham had testified in federal court that he was innocent but believed he was possessed by an evil spirit that made him do things he does not remember.

During an initial investigation Durham confessed to sexually molesting and raping as many as 10 orphans during a mission trip to Kenya, claiming a demon named Luke made him do it.

In text messages at the time of his crimes, Durham claimed that a demon named Luke was coming to him at night, once texting:

Every night Luke gets what Luke wants

Speaking after the sentencing, Acting U.S. Attorney Mark Yancey said:

Mr. Durham took advantage of his position as a ministry volunteer to sexually assault multiple children in Kenya. The significant sentence imposed today will remove the threat of any other children being exploited by him.

Speaking out in court in Oklahoma City on Monday, Durham asked the court for mercy before declaring:

Judgment from God is central, not the judgment of man. I do not fear God’s judgment.

Durham’s attorney Stephen Jones said he plans to appeal the convictions.

For more on this story see Matthew Durham.