A polygamous religious leader who claimed more than 20 spiritual “wives” including 10 underage girls faces decades in prison at his sentencing on Monday for forcing girls as young as nine years old to submit to criminal sex acts with him and other adults.

Samuel Bateman, whose small group was an offshoot of the sect once led by Warren Jeffs, has pleaded guilty to a years-long scheme to transport girls across state lines for his sex crimes, and later to kidnap some of them from protective custody. His plea agreement called for 20 to 50 years in prison, though each conviction carries a possible life sentence.

But first, a federal judge will hear from a doctor who evaluated Bateman’s competency. The question could determine whether the sentencing goes forward or Bateman is remanded to state custody for psychiatric treatment until he’s deemed mentally fit to assist in his defense, his attorney Brian Russo said.