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A timeline

Saturday morning: Ismaaiyl Brinsley reportedly shoots former girlfriend in Maryland and takes her cellphone. She survives.

Later Saturday: Traveling by bus to New York, Brinsley uses the cellphone to post updates on his plans for the rest of the day. "I'm Putting Wings On Pigs Today," Brinsley apparently writes on an Instagram posting, where he also references the death of Eric Garner, a black man killed in a confrontation with New York police. "They Take 1 Of Ours, Let's Take 2 of Theirs."

1:30 p.m.: The mother of the woman Brinsley is suspected of shooting in Maryland alerts police of the messages. Investigators in Maryland scramble to determine where they had been posted from. Soon after, they locate the posts and find a cellphone carried by Brinsley in Brooklyn.

2:10 p.m.: Baltimore County authorities call the 70th Precinct in Brooklyn and tell them of the threatening messages. They fax a wanted poster to the precinct, naming Brinsley.

2:45 p.m.: The information is circulated throughout the New York Police Department.

2:47 p.m.: Brinsley approaches the officers and fatally shoots them in their car in the 79th Precinct, several miles north of where his cellphone had been located by police.

2:50 p.m.: The same information that was shared with the 70th Precinct is sent from Baltimore County to the real-time crime center at New York City Police headquarters. By then it was too late.

NEW YORK TIMES