"When you're trying to take care of a scene and you're trying to protect that — you know, shell casings, different things like that — and we're dealing with other issues, I think that makes it a little more difficult for us to do our job and it certainly makes it more difficult for us to do our job in a timely fashion," he said.

"We really do need to get to the point where we can at least wait for certain facts to materialize before we jump to conclusions, before we make attributions,before we become cynical," he added. "I've already seen through social media that this officer stopped him, questioned him, frisked him and then killed him in cold blood — well, that's not what you're going to see when you see the video."

Hoskins, at his news conference said, "You can't compare this to Ferguson or the Garner case in New York." He said the videotape showed Martin pointing a gun at the officer. He said the city would conduct its own complete investigation, separate from the St. Louis County Police investigation.

"Our overall goal is to project the truth to residents," Hoskins said.

Among the department's 31 officers, the mayor said, 17 or 18 are African-American. About 75 percent of the command staff are black, in addition to the mayor, police chief and other city officials, Hoskins added.