NEW YORK — Federal prosecutors will not bring criminal charges in the case of an unarmed black teenager who was shot to death in his home by a white New York City police officer, officials said Tuesday.

The US attorney’s office in Manhattan said prosecutors found insufficient evidence to pursue federal charges in the 2012 death of Ramarley Graham and have officially concluded their investigation.

The 18-year-old was shot in the bathroom of his Bronx home by an officer who had barged inside during a drug investigation.

He was killed in front of his grandmother and 6-year-old brother.

In a statement Tuesday, US Attorney Preet Bharara said his office conducted a thorough and independent investigation, but determined ‘‘there is insufficient evidence to meet the high burden of proof required for a federal criminal civil rights prosecution.’’

Richard Haste, the officer who shot Graham, said he fired his weapon because he thought he was going to be shot. No weapons were found in the apartment.

Associated Press