In a letter sent a day before the fourth anniversary of Garner's killing on a city sidewalk by police trying to arrest him for peddling untaxed cigarettes, the police department decried the pace of the Justice Department's civil rights investigation.

Cellphone video footage of Garner repeatedly saying "I can't breathe!" to the officer whose arm is around his neck helped focus national attention on police killings of unarmed black men and fueled the burgeoning Black Lives Matter movement.