The gunman who fatally ambushed two police officers in their squad car had a long criminal record, a hatred for police and the government, and an apparent history of mental instability that included an attempt to hang himself a year ago, authorities said.

Moments before opening fire, Ismaaiyl Brinsley approached people on the street in Brooklyn and asked them to follow him on Instagram, then told them, "Watch what I'm going to do", Chief of Detectives Robert Boyce said.

A portrait of the Brooklyn-born gunman emerged as big-city police departments and union leaders around the United States warned officers to change their routines and insist on extra backup a day after Brinsley carried out what he portrayed online as retaliation for the killings of black men at the hands of white police officers.

Brinsley was black; the two officers were ethnically Asian and Hispanic.

Tense time

The killings come at a tense time. Police across the country have been criticized for months for their tactics, following Eric Garner's death in a New York officer's chokehold and Michael Brown's fatal shooting in Ferguson, Missouri. Protests erupted in recent weeks after grand juries declined to charge the white officers involved.

Investigators were trying to determine if Brinsley had taken part in any protests over the deaths of Brown and Garner, whose names he invoked in his online threat, or simply latched on to the cause for the final act in a violent rampage.

Brinsley, 28, had at least 19 arrests in Georgia and Ohio, spent two years in prison for gun possession and had a troubled childhood so violent that his mother was afraid of him, police said. He ranted online about police and the government and expressed "self-despair and anger at himself and where his life was", Boyce said.

Boyce said Brinsley's mother believed he had undiagnosed mental problems and may have been on medication at some point, but detectives were still trying to determine if he had a mental illness.

On Saturday afternoon, Brinsley approached a squad car from behind in Brooklyn's Bedford-Stuyvesant neighborhood and fired four shots, killing Officers Rafael Ramos and Wenjian Liu. He then ran into a subway station and committed suicide.

The siege mentality was evident in several memos circulating at the New York Police Department.

A union-generated message warned police officers that they should respond to every radio call with two cars - "no matter what the opinion of the patrol supervisor" - and not make arrests "unless absolutely necessary". The president of the detectives union told members in a letter to work in threes when out on the street, wear bulletproof vests and keep aware of their surroundings.

"Cowards such as yesterday's killer strike when you are distracted and vulnerable," the letter read.

AP - AFP - Reuters

(China Daily 12/23/2014 page12)