Boston police officers trying to stop a deranged man with a pellet gun who'd stolen a police cruiser should have called in a mental-health professional rather than shooting him dead, his widow argues in a lawsuit filed last week.

Marquis Barker, 37, was fatally shot on Nov. 21, 2007 in a Walgreens parking lot at Morton and Norfolk streets. Police say he appeared to be reaching for what officers at the time thought was a semi-automatic gun - as he sat in the police cruiser he'd stolen moments before outside his Fuller Street home, where he'd disregarded commands from other officers to drop the weapon he'd been waving around.

In her lawsuit, filed in US District Court in Boston, Kim Sanders Barker said that after her husband - "foaming at the mouth" - left their home with the gun, she called 911 and told the dispatcher her husband had suffered a breakdown and was outside with a non-lethal pellet gun. Barker alleges that officers who knew about the Suffolk County correctional officer's impaired condition didn't notify other arriving officers, but that that shouldn't have mattered because: "Although Barker's diminished mental and physical capacity was open and obvious, at no time did Officer Donahue or Officer McHale contact BPD dispatch to request medical or psychiatric assistance for Barker or request a crisis negotiator."

Among the obvious signs of Barker's mental issues, the suit says: Outside his house, Barker held the gun to his head and demanded that police shoot him immediately.

In a 2009 report, the Suffolk County District Attorney's office cleared the officers, saying Barker's pellet gun was a model designed to look identical to a SIG combat pistol and that they legitimately feared for their lives when he disregarded orders to get out of the car and instead appeared to be getting ready to fire the weapon.