MADISON, Wis. — A Wisconsin prosecutor won't charge four officers who fatally shot a man who opened fired on four co-workers at a software company last year.

Dane County District Attorney Ismael Ozanne said Monday the two sheriff's deputies and two Middleton police officers who shot 43-year-old Anthony Tong on Sept. 19 were justified.

Tong, a WTS Paradigm employee, opened fire in the company's Middleton headquarters and wounded four of his co-workers, three seriously. Tong died in a shootout with the officers minutes after the attack began.

Ozanne said Monday that Tong's motive is still unclear and it's possible that investigators will never know. He says Tong had a long history of schizophrenia and wasn't allowed to own guns, but he purchased the parts to build one and avoid a background check.