HASTINGS, Neb. (AP) — A Nebraska man has been sentenced to life in prison for helping his mother fatally stab her boyfriend’s 68-year-old mother.

Twenty-four-year-old Andrew Casterline of Guide Rock was sentenced Monday. He was convicted in September of first-degree murder, use of a deadly weapon to commit a felony and burglary in the October 2013 death of Virginia Barone.

Authorities say Casterline and his mother, Shelly Casterline, stabbed Barone 22 times and hid her body beneath boards in her home.

Shelly Casterline tells authorities she killed Barone after the older woman angered her. She says her son wasn’t there but prosecutors say cuts on his hands indicated he wielded a knife.

His mother was sentenced to life in prison in September.