The white police officer who fatally shot unarmed black teenager Michael Brown in the US town of Ferguson has resigned with immediate effect.
Darren Wilson, who had been on administrative leave since the killing, told a newspaper he did not want to put the lives of police colleagues at risk.
Rioting rocked Ferguson and other towns this week after a jury decided he should not be charged over the killing.
The 9 August shooting in the St Louis suburb and the decision not to charge Mr Wilson triggered a nationwide debate over relations between black communities and law enforcement.
The St Louis Post Dispatch reported that Mr Wilson, 28, had decided to step down after his police department received threats of violence if he stayed on as an employee.
A resignation letter, claiming to be from the officer published in the newspaper, read: “I have been told that my continued employment may put the residents and police officers of the City of Ferguson at risk, which is a circumstance that I cannot allow.
“For obvious reasons, I wanted to wait until the grand jury made their decision before I officially made my decision to resign.
“It was my hope to continue in police work, but the safety of other police officers and the community are of paramount importance to me. It is my hope that my resignation will allow the community to heal.”
In a subsequent telephone interview on Saturday evening, the paper quoted Mr Wilson as saying: “I’m resigning of my own free will. I’m not willing to let someone else get hurt because of me.”
Ferguson’s Mayor James Knowles later said that Mr Wilson had resigned without receiving any severance payments.
At a news conference, the mayor also announced incentives to bring more African-Americans into the Ferguson police force, which is currently overwhelmingly white.
Many in the African-American community had called for Mr Wilson to be charged with murder, but after three months of deliberation a Missouri grand jury – of nine white and three black members – made no recommendation of charges.
The family of Mr Brown have said they felt “crushed” by the decision.
The state prosecutor said physical evidence had contradicted some of the witness statements.
The decision means Mr Wilson will not face state criminal charges over the shooting. However, the US justice department has launched a federal investigation into whether Mr Wilson violated Mr Brown’s civil rights.