OMAHA, Neb. (AP) — An Omaha man pleaded guilty Wednesday to killing his mother and his 4-year-old half brother, avoiding the death penalty.

Roberto Martinez-Marinero, 25, pleaded guilty to two counts of first-degree murder in the May deaths of 45-year-old Jesus Ismenia Marinero and 4-year-old Josue Ramirez-Marinero. After entering the plea in Douglas County District Court, he was sentenced to a mandatory term of life in prison.

Prosecutors say Martinez-Marinero stabbed and beat his mother with a baseball bat on May 5 at his home in a fit of rage over an ongoing dispute over money. Her body was found the next day in a southeast Omaha ditch.

Police say that after fatally attacking his mother, Martinez-Marinero took his mother's two youngest children — his half brothers — in an attempt to eliminate witnesses to his mother's attack. Police say he dumped his then-11-month-old half brother in a La Vista dumpster. The child was found hours later by a passer-by, bruised and wearing only a diaper, but otherwise uninjured.

Officials say Martinez-Marinero also threw 4-year-old Josue from an Elkhorn River bridge to his death. The boy's body was found in the river days later.

Martinez-Marinero's live-in girlfriend at the time also is charged. Police believe Gabriela Guevara, 25, helped Martinez-Marinero load his mother in a car and dump her. Guevara also was with Martinez-Marinero when he disposed of his half brothers, investigators have said.

Guevara has pleaded not guilty to five counts of being an accessory and has asked a judge to throw out her statements to police.