U.S. Attorney Walt Green says federal authorities don't have a timetable for completing their investigation of a black man's fatal shooting during an altercation with two white Baton Rouge police officers.

Green said in a written statement Tuesday that the Justice Department has dedicated hundreds of hours to its investigation of Alton Sterling's July 5 shooting and is "committed to taking all necessary steps to reach a just result." He says a team of career federal prosecutors, FBI agents and support personnel have devoted hundreds of hours to the investigation.

Sterling was shot and killed by one of the two officers who responded to a caller's complaint that Sterling had threatened the caller with a gun outside a convenience store. Cellphone video of the deadly encounter quickly spread on social media. During a City Hall rally last month, one of Sterling's aunts expressed frustration with the pace of the investigation.

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