Three current and former Chicago police officers were indicted on Tuesday on felony charges for conspiring to cover up the shooting death of a black teenager by a white officer, prosecutors said.

The indictments stem from a 2014 incident in which Laquan McDonald, 17, was shot to death. A video of the shooting, released in 2015, sparked days of protests and thrust Chicago into a national debate over the use of excessive force by police against minorities.

Detective David March and officers Joseph Walsh and Thomas Gaffney were each charged with conspiracy, official misconduct and obstruction of justice, the special prosecutor, Patricia Brown Holmes, said.

“The indictment makes clear that these defendants did more than merely obey an unofficial 'code of silence,' rather it alleges that they lied about what occurred to prevent independent criminal investigators from learning the truth,” Holmes said in a statement.

A police union spokesman declined to comment. It was not immediately known if March, Walsh and Gaffney had hired attorneys. A lawyer for the McDonald family did not immediately respond to a request for comment.

All three officers were on scene the night of the shooting, Holmes told reporters. Chicago police representatives said Walsh and March are no longer with the force and that Gaffney will be suspended without pay.

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The three officers conspired to conceal the true facts surrounding McDonald's killing in order to protect their fellow officer from criminal investigation and prosecution, the indictment said. They lied about what happened and mischaracterized the video recordings, which they knew would lead to a criminal investigation and likely criminal charges, it said.

Jason Van Dyke, the Chicago police officer accused of murder in the McDonald shooting, was charged in March with 16 new counts of aggravated battery. Van Dyke pleaded not guilty to the 16 counts. He pleaded not guilty to murder in 2015 and is awaiting trial.

When asked if others might face charges, Holmes said the matter is still being investigated.

March, 58, and Walsh, 48, were police veterans of more than 30 years and about 20 years, respectively. Gaffney, 43, has about 20 years in the department. All are expected to be arraigned on July 10.

Chicago police last month finalised stricter limits on when officers can use firearms and other force, the latest attempt to reform a department roiled by misconduct and criticism in the wake of McDonald's death.