Site where two New York Police officers were shot dead in Brooklyn
Site where two New York Police officers were shot dead in BrooklynReuters

The gunman who fatally ambushed two police officers in their car in Brooklyn on Saturday invited passersby to watch his attack, The Associated Press (AP) reported Sunday.

Moments before opening fire, the suspect, Ismaaiyl Brinsley, approached people on the street 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 country warned officers to change up their routines and insist on extra backup a day after Brinsley carried out what he portrayed online as retaliation for the slayings of black men at the hands of white police.

Brinsley was black; the slain officers were Asian and Hispanic.

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

They said he traveled frequently between the South and New York, where he fathered a child in Brooklyn, and had been in the city earlier in the week.

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, according to AP.

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 section and fired four shots, killing Officers Rafael Ramos and Wenjian Liu. He then ran into a subway station and committed suicide.

The slayings dramatically escalated tensions that have simmered for months over police killings of blacks.