Prosecutors are investigating the death of a St. Louis suspect fatally shot by police, after an autopsy showed the 18-year-old was shot in the back.

Circuit Attorney Jennifer Joyce announced Friday a simultaneous investigation separate from police after the autopsy results on Mansur Ball-Bey were announced, the St. Louis Post-Dispatch (http://bit.ly/1KCrBeV ) reports. The past practice has been for the prosecution to await the police results before proceeding.

"I want nothing more than to reach the right conclusion here," Joyce said. "I want there to be peace in this city."

The shooting on Wednesday set off an evening of violent outcry, with authorities saying at least nine people were arrested and property damaged. It also came on the heels of violence that marred the one-year anniversary of the day Michael Brown was killed by a white officer in nearby Ferguson — a killing that sparked protests, the "Black Lives Matter" movement and a national debate over police treatment of African-Americans.

Attorney Brian Millikan, who is representing the officer who fired the deadly shot and another officer who also opened fire, said the reason for the wound's location was because the officers were in separate positions when Ball-Bey turned toward one officer with a gun. He said one of the officers was firing in defense of his partner.

"Both policemen had multiple opportunities to engage this guy and they didn't do that because he never pointed a weapon at them until he got to the rear yard," Millikan said of his clients, with whom he sat Friday as they gave their statements to detectives at police headquarters. "But when (Ball-Bey) turns toward (one officer) with a gun that has an extended clip with a 30-round magazine, the policemen have no choice but to pull the trigger."

Chief Sam Dotson said at a press conference Friday that he could not yet conclude whether the shooting of Ball-Bey was justified because the facts were still developing and urged the public to withhold judgment.

"There is no benefit to not putting out the complete truth," Dotson said. "What the community has to understand is that the complete truth takes time to put together."

Jermaine Wooten, an attorney for Ball-Bey's family, said witnesses and family members had told him Ball-Bey was unarmed.

"I told them, 'If you want me to represent you, don't lie to me. Did he have a gun?' And they all said, 'No,'?" Wooten said.

But Dotson said that apart from two officers involved in the shooting, one civilian witness corroborated official statements that Ball-Bey had pointed a gun at officers. Dotson added that he welcomed Joyce's review, adding that his department was accustomed to conducting joint investigations with other agencies, such as the FBI.

"It's not a problem," he said of Joyce's involvement. "What it does is speeds up the investigative process and the final report, so the public gets answers more quickly and I think that's a good thing."