CLAYTON, Mo. — On the fifth anniversary of Michael Brown's death in Ferguson, his father urged St. Louis County's top prosecutor Friday to reopen the investigation into the white police officer who fatally shot the black and unarmed 18-year-old.

Before a memorial service in the Ferguson street where a white police officer fatally shot his son on Aug. 9, 2014, Michael Brown Sr. addressed reporters outside of the St. Louis County Justice Center in the St. Louis suburb of Clayton.

"Justice has not been served," Brown, 41, said as he was flanked by about three dozen supporters. "My son deserved to live a full life. But a coward with a badge ... chose not to value his life.

"My son was murdered in cold blood, with no remorse and no medical treatment," said Brown, who has never accepted the officer's claim that he had acted in self-defense.

Prosecuting Attorney Wesley Bell, the county's first black prosecutor, took office in January after his stunning victory over seven-term incumbent Bob McCulloch.

McCulloch drew criticism for his handling of the investigation into the Michael Brown shooting, with detractors accusing him of guiding the grand jury to its decision not to indict the officer, Darren Wilson, which came in November 2014, three months after Brown's death.

The U.S. Department of Justice under then-President Barack Obama also declined to charge Wilson, who resigned within days of the grand jury decision announcement.

In a statement to The Associated Press, Bell would not say whether his office would reopen the case, but he said it "is doing everything (it) can to understand the underlying issues that contributed to the tragic death of Michael Brown."

Bell said his office is working with police "to implement policies and reforms that meaningfully address those issues, and help this community and this region heal." He said he is also forming a special unit within his office to look at officer-involved shootings and potential cases of wrongful convictions.

Brown's mother, Lesley McSpadden, also has urged Bell to reopen the case.

Later Friday, a few hundred people gathered for a memorial service on Canfield Drive at the site of the shooting. The service included 4 1/2 minutes of silence, a symbolic reference to the 4 1/2 hours Brown's body remained on the street after the shooting.

On the day he died, Brown and a friend were walking down the middle of Canfield Drive when Wilson told them to move to the sidewalk. An exchange of words led to a fight inside Wilson's SUV. Brown got out and began to ran, then turned around to face the officer.

Wilson told investigators that he shot Brown — who was 6 feet, 4 inches tall and weighed 290 pounds (131 kilograms) — in self-defense. Some people in the Canfield Green apartment complex near the shooting initially claimed that Brown had his hands up in surrender, but the grand jury found no evidence to confirm that.

The shooting led to weeks of protests that included looting and violent confrontations between demonstrators and police officers, many in riot gear and with military-style weapons. Protests escalated again after the grand jury announcement.

Although the Justice Department declined to indict Wilson, it did issue a report citing racial prejudice in the Ferguson Police Department and a municipal court system that made money through court fines and legal fees — costs largely borne by black residents. A consent agreement signed in 2016 requires significant reforms.

Bell, 44, is among a wave of progressive prosecutors elected in recent years. His office seeks alternatives to incarceration when possible, including for some non-violent drug crimes. He has stopped prosecuting most marijuana possession cases and reduced the use of cash bail.

Bell would face no restrictions in re-examining Brown's death for potential murder charges. Wilson was never charged and tried, so there would be no double-jeopardy, and there is no statute of limitations for bringing murder charges.

It would be unusual, but not unheard of, for a prosecutor to reopen an old case that's been so thoroughly examined. A Philadelphia prosecutor initially declined to charge actor Bill Cosby with sexual assault, but a new prosecutor was elected and Cosby was charged and convicted.