A 25-year-old Omaha man has pleaded guilty to killing his mother and his 4-year-old half brother to avoid the death penalty.

Roberto Martinez-Marinero pleaded guilty Wednesday in Douglas County District Court to two counts of first-degree murder in the May 5 deaths of 45-year-old Jesus Ismenia Marinero and 4-year-old Josue Ramirez-Marinero.

He is sentenced to a mandatory term of life in prison.

Prosecutors say Martinez-Marinero repeatedly stabbed and beat his mother in a dispute over money. He dumped her body in a ditch, left his 11-month-old half brother in a dumpster and threw his 4-year-old half brother to his death from a bridge over the Elkhorn River.

A passer-by discovered the baby after hearing noises coming from the trash bin. The boy, wearing only a diaper, suffered only bruises.