Federal prosecutors have decided not to pursue criminal charges against a white New York City police officer accused of shooting an unarmed black teenager to death in the Bronx in 2012 in a case that has drawn attention from civil rights advocates.

Manhattan U.S. Attorney Preet Bharara's statement marked the end of an investigation into the death of Ramarley Graham, 18, who was shot inside the bathroom of his Bronx apartment after being followed by police officers.

Bharara's office said there was "insufficient evidence" to pursue charges against Richard Haste, the officer who shot Graham, on Feb. 2, 2012. The evidence indicated Haste believed Graham had a firearm and was reaching for it, the statement said.

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Bharara's statement came shortly after he met with Graham's parents, Constance Malcolm and Frank Graham, who held a press conference along with more than a dozen supporters outside the U.S. attorney's offices after the meeting.

Malcolm called the decision a "slap in the face," saying Haste "murdered my son."

"Same as usual, black life doesn't matter," Frank Graham said, adding that they would push for Haste's termination.

Bharara's announcement comes amid heightened attention to the use of police force against minorities following nationwide protests in cities such as Baltimore and Ferguson, Missouri.

New York City police officer Peter Liang was convicted of manslaughter last month for his shooting of an unarmed black man, 28-year-old Akai Gurley, in the dark stairwell of a Brooklyn housing project.

In 2014, a grand jury declined to charge an officer in the chokehold death of another unarmed black man, Eric Garner, sparking citywide protests. A federal investigation is ongoing.

Haste was indicted by a grand jury in the Bronx on state manslaughter charges in June 2012. A judge later dismissed the indictment, saying prosecutors gave the grand jury improper instructions.

A second state court grand jury in August 2013 decided not to re-indict Haste.

Police have said that several officers who had seen Graham on the street - including Haste - suspected he had a gun because of the way he moved his hands near his waist.

Haste and a partner followed Graham to his apartment building and kicked down his apartment door. Haste shot Graham in the chest in a bathroom, police said.

In January 2015, New York City agreed to pay $3.9 million to resolve a federal lawsuit by the Graham family over the killing.