Before a mostly black audience, Captain Johnson, who is African-American, spoke of his own “black son, who wears his pants saggy, wears his hat cocked to the side and has tattoos on his arms.” He added, “That’s my baby.”

“Michael’s going to make it better for our sons so they can be better black men,” he said, predicting that the treatment of black youths here would somehow change. “We need to pray. We need to thank Michael for his life. And we need to thank him for the change that he is going to make.”

Time and again, he won applause. But in a vivid display of the challenges faced by the authorities in this tumultuous city of 21,000 that has become the center of a national debate about race and policing, a large crowd outside continued to protest Mr. Brown’s death. The shooting of the teenager on Aug. 9 by a white officer, Darren Wilson, is the subject of inquiries by the Federal Bureau of Investigation and the St. Louis County police.

Several demonstrators held signs reading “Stop racist police killing,” while many others joined in the chant that has echoed through this city’s streets for days: “Hands up! Don’t shoot!” Hours earlier, just after a midnight curfew went into effect on Saturday, police officers dressed in riot gear and driving heavily armored vehicles engaged in a new clash with angry demonstrators. One person threw a bottle bomb that lit the street ablaze and left a lingering scent of gasoline. Before long, a police caravan, with lights flashing, began rolling slowly toward the protesters.

“You are violating the state-imposed curfew,” an officer said over a loudspeaker. “You must disperse immediately or you’ll be subject to arrest and or other actions.” The crowd did not back down, cheering louder. Eventually a canister of tear gas was lobbed into the crowd. Smoke filled the air. Some people ran away from the police. Bottles crashed onto the pavement. Captain Johnson said the heavy police response had been prompted by reports of armed people at a barbecue restaurant.