NEW YORK - Law enforcement sources say the New York native behind Monday's mass shooting at the Washington Navy Yard had a history of serious mental illness.

According to officials, 34-year-old Aaron Alexis, a former Navy reservist who was born in Queens, was being treated since last month by the Veterans Administration for his mental problems, including paranoia, a sleep disorder and hearing voices.

Alexis killed 12 people and and wounded eight others before being fatally shot by police, investigators say. He also had previous run-ins with the law, including an arrest for shooting the rear tires of a car during a road rage incident and an arrest for disorderly conduct.

Officials are focusing part of the investigation on the Brooklyn home where Alexis' mother and other close family members live.

They are questioning the family and have cordoned off the their home, located in the Bed-Stuy section of the borough. However, News 12 has no confirmation as to whether Alexis ever lived there.