He was married, employed and had a PhD and no criminal history, police said.

As he walked away, he shot Ramona Cooper, 60, a staff sergeant in the Air Force, three times in the back, killing her.

He then shot retired Massachusetts state trooper Dave Green, 68, multiple times. When police arrived on the scene they exchanged gunfire with Allen, killing him.

Investigators said they found "troubling white supremacist rhetoric" in the gunman's handwriting.

Her office's statement said: "This individual wrote about the superiority of the white race. About whites being 'apex predators'. He drew swastikas."