Gutierrez turned himself in to Covina police around 4:30 p.m. Tuesday, and was booked on suspicion of murder. He is expected to be arraigned Thursday.
Investigators say Gutierrez's grandfather called police after he heard a gunshot inside his home on South Brightview Drive Monday afternoon.
Patrol officers who responded to the call found Hassan in a bedroom, with significant head trauma. She was pronounced dead at the scene.
Police say a motive is still unclear.
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