The parents of an unarmed black teenager killed by a white New York City police officer exactly four years ago Tuesday have written a letter to the mayor and his wife saying the city has waited too long to fire the officer.

In this June 13, 2012, file photo, the parents of Ramarley Graham, Constance Malcolm, and Frank Graham, make a statement outside the courthouse in New York. (AP Photo/Seth Wenig, File)

Ramarley Graham was 18 when he was shot once in the bathroom of his Bronx home by an officer who had barged inside during a drug investigation.

The teen's parents, Constance Malcolm and Franclot Graham, said in their letter to Mayor Bill de Blasio and his wife, Chirlane McCray, that they were appealing to them as fellow parents.

"Four years have passed, and there has been no explanation, no justice, no morality, and thus no sense of legitimacy," said the letter, according to a copy obtained by The Associated Press. "It is sickening for any penny of our tax dollars -- or any New Yorkers' for that matter -- to be received by any of the officers who were responsible for the murder of our son, and the cover-up."

Last year, the family settled a civil lawsuit against the city for $3.9 million.

The officer who shot Graham, Richard Haste, was initially indicted in the Bronx on a state manslaughter charge but a judge dismissed the case after determining prosecutors improperly instructed grand jurors.

A new grand jury cleared the officer.

After the shooting, Haste was stripped of his badge and gun and assigned to the department's fleet services division, officials said, but an internal disciplinary proceeding against him has been on hold pending the outcome of a federal investigation.

In that time, Haste has received raises guaranteed by his union contract.

Haste has said in a court filing that he fired because he believed Graham had a gun and was about to shoot. No weapon was ever found.

"We are a nation and city of laws where justice demands that an individual is innocent unless proven guilty in a court of law," said Patrick Lynch, president of the Patrolmen's Benevolent Association, which represents Haste. "Regardless of the facts in this case, a family lost a loved one and they have our sympathy, but grief and emotion can never override due process."

In New York, the mayor doesn't have the power to summarily fire police officers.

Disciplinary matters are adjudicated in an internal police process and the commissioner has the ultimate say in an officer's fate.

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