The U.S. Department of Justice and the FBI have opened an investigation into the “facts and circumstances” surrounding the killing of Trayvon Martin, the unarmed teenager shot and killed last month by a neighborhood watch captain in an Orlando suburb.

The department will “conduct a thorough and independent review of all evidence and take appropriate action at the conclusion of the investigation,” according to a statement late Monday.

The announcement comes as the drumbeat around the case continues to grow, becoming national news and shining a brighter media spotlight on the city of Sanford, where the killing occurred, and its police department, which handled the initial investigation that so far has failed to bring charges.

Martin, 17, was shot to death on Feb. 26 by George Zimmerman, a neighborhood watch captain who told police he fired in self-defense. Zimmerman confronted the teen after calling 911 and reporting Martin as a “suspicious person.” Though a dispatcher told Zimmerman not to follow the teen, Zimmerman confronted him nevertheless, police said. Martin died from a gunshot wound to the chest.

Police questioned Zimmerman and released him without charges. Zimmerman was licensed to carry a gun and police said they found no evidence to contradict his self-defense claim.