NEW YORK (CBSNewYork/AP) — A police officer who shot an unarmed black teenager to death in the bathroom of his Bronx apartment in 2012 has resigned, officials say.

In a statement released Sunday, the department confirms that Police Officer Richard Haste decided to quit “upon being informed that on Friday, March 24 the Department Trial Commissioner found him guilty on all counts and recommended his employment be terminated.”

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“Police Commissioner O’Neill has fully concurred with the findings and recommendations of the Trial Commissioner,” the statement concluded.

Officer Richard Haste initially faced a criminal manslaughter charge in Graham’s death, but the criminal case was dismissed because of a procedural error and a new grand jury declined to indict.

Federal prosecutors also declined to bring charges, saying there was no evidence to refute Haste’s claim that he shot the teen because he mistakenly believed he was reaching for a gun.

“My son Ramarley was gunned down and murdered by NYPD Officer Richard Haste over 5 years ago,” Graham’s mother Constance Malcolm said in a statement responding to Haste being allowed to resign Sunday. “Richard Haste should have been in prison but instead of even firing him, the de Blasio administration just let him resign. This is just another example that the de Blasio administration doesn’t care about justice and accountability. Every step of the way, the Mayor and NYPD have dragged their heels and have refused to hold officers accountable for murdering my son. 5 years after my son was killed, they made me take off work to sit through a trial while in the end, they let Richard Haste off the hook, and are continuing to give the other officers responsible for killing Ramarley and other misconduct every opportunity to escape accountability. They haven’t even scheduled the trials for Sgt Morris or McLoughlin – the only 2 officers that even have internal charges against them. How is my youngest son supposed to trust and believe in cops when he saw they murdered his brother in front of him and there is zero accountability?”

Mayor Bill de Blasio released a statement late Sunday in response to Haste’s resignation, saying “The NYPD disciplinary trial of Richard Haste ended with the right decision: termination.”

“Ramarley Graham was a son, a friend, and most importantly, a young man with his whole life left to live,” the mayor continued. Nothing can take away the profound pain left after his loss, but I hope the conclusion of this difficult process brings some measure of justice to those who loved him.”

In the proceedings, the NYPD firearm discharge review board ruled the shooting itself was justified, but that Haste didn’t use the proper tactics.

“If the shooting is justified, the tactics should be justified and in this case they’re looking for a scapegoat because of the unfortunate outcome of the shooting,” Haste’s lawyer, Stuart London, said during the departmental disciplinary trial.

The shooting stemmed from an investigation of drug dealing in Graham’s Bronx neighborhood.

A narcotics team had a neighborhood convenience store under surveillance. When Graham exited the shop with friends, investigators reported over their radios that they thought they saw a gun in the waistband of his pants.

On the stand, Haste recounted how he got out of his police van during a drug probe in Graham’s neighborhood and followed the teenager into his apartment. He went around and got in through a neighbor’s home, then unlocked the front door for other members of his team. They walked up the stairs tensely, watching for suspects and looking for cover. He said he saw Graham sidestep into a bathroom, and he leaned inside to face him.

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“He’s in front of me,” he said. “And I want to take him into custody. I want to put an end to this,” he said. Haste yelled, “Show me your hands!” but Graham instead reached deeper into his pants and yelled obscenities, Haste testified.

After he pulled the trigger, he saw Graham’s grandmother and little brother screaming in the hallway, and a tan boot pointed up out of the bathroom door. He was ordered outside by other officers.

No gun was found, but a bag of marijuana was floating in the toilet.

Haste said he had been in similar situations more than 10 times before but had never pulled the trigger.

Haste said he reacted using the best of his training experience from the department.

“I don’t think there is a perfect world,” he said.

Haste’s attorney argued earlier that there are no specific guidelines to follow in these situations.

“What’s important to remember is that these decisions were made in milliseconds,” London said.

London called Haste a “hero officer who was attempting to take a weapon off the street.”

De Blasio said Sunday that his administration “has taken unprecedented steps to strengthen the relationship between police and our neighborhoods, and increase transparency through important reforms — from retaining the entire force, to deploying body cameras on officers.”

“We are relentless in our efforts to ensure that lives will be saved as a result of the unspeakable loss of Ramarley Graham,” the mayor concluded.

Graham’s mother will be holding a press conference outside of NYPD Headquarters Monday at 11:30 a.m. in response to the city allowing Haste to resign.

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(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)