Continued from page 1

The families of Trayvon Martin and Oscar Grant — two other black males whose deaths at police hands prompted national outcries — also spoke at the rally, which had been planned before the Brown killing.

Mr. Clay said he’s not concerned about the funeral reigniting tensions that have boiled over in recent weeks, but acknowledged that would be a possibility if “we do not bring justice to this situation.”

“I guess what I’m most concerned about — and I made a promise to Michael Brown’s parents that I would do everything to bring all of the resources of the federal government to this investigation so that it’s transparent, so that it’s a viable investigation and we get to the truth,” he said.

“I’m more concerned that if we do not get to the truth and get to what actually happened and bring justice to this situation, then there’s going to be a problem in the street,” he said.

A grand jury has been formed to hear evidence about possible charges to be brought against Mr. Wilson, and the U.S. Department of Justice is conducting its own civil rights investigation.

But in a suggestion that some already are seeing the state investigation as tainted, Mr. Nixon was pressed repeatedly to defend Sunday his decision to keep the investigation in the hands of St. Louis County prosecutor Bob McCulloch.

The Brown family and some protesters have said Mr. McCulloch, who is white, cannot be trusted with the investigation because both his parents and other relatives have worked for the St. Louis police and/or because his father was killed in the line of duty by a black crime suspect.

“Well, he’s democratically elected by overwhelming numbers, and re-elected, and re-elected,” Mr. Nixon said on CNN, while parrying demands from host Candy Crowley for “1000 percent confidence.”

Mr. Clay said Attorney General Eric H. Holder Jr. brought a “calming force” when he visited the area last week.

“And it kind of reinforced people’s trust that at least on one track there will be an aboveboard, thorough investigation on the part of the federal government, especially with the FBI here as well as the U.S. Department of Justice,” he said on ABC’s “This Week.”

The White House will send a three-person delegation to the Monday morning service at Friendly Temple Missionary Baptist Church in St. Louis.

Phillip Swarts contributed to this article.