King County prosecutors previously declined to file charges against Birk, who resigned from SPD following an internal investigation into the shooting.
The Department of Justice—which recently found a pattern of civil rights violations in the Seattle Police Department—investigated Birk's shooting of Williams, but did not find that Birk had violated Williams' civil rights when he fatally shot him four times on a downtown street. An SPD investigation found that Birk's shooting of Williams was unjustified under department policy.
Federal authorities have previously charged police officers in other jurisdictions for egregious civil rights violations. In one recent case in New York City, the DOJ filed charges against a police officer who falsely arrested a black man for resisting arrest, and the later bragged about fabricating a police report in the case.
A Department of Justice spokesman declined to discuss the status of the case.
UPDATE: A statement from the Department of Justice explains that "prosecutors must establish, beyond a reasonable doubt, that a law enforcement officer willfully deprived an individual of a constitutional right, meaning with the deliberate and specific intent to do something the law forbids," and says "evidence [against Birk] was insufficient to prove, beyond a reasonable doubt, that the former Seattle Police Officer acted willfully and with the deliberate and specific intent to do something the law forbids. "