“Our youth are out here without guidance, without leadership,” Ms. Wood told Captain Johnson. “It’s important that they know there is an order.”

When Ms. Wood finished, Captain Johnson patted her right shoulder and said softly: “I thank you. I thank you for your passion, and we’re going to get better.”

He then joined a group of passing protesters, marching with them as his eyes scanned the roadway. “I know a lot of them,” he said. “Our police department, we have to be reflective of our community, and that’s why we’re all out here.”

Jessica Daniel, who was marching with her young children, said she had listened to speeches by Ms. McCaskill and Mr. Nixon and perceived a change. “The whole tone just turned around,” she said. “Now I feel like they are letting us know they think it’s tragic, too. It’s a beautiful thing.”

Outside a restaurant, London’s Wing House, Kristopher Conner said he was upset both by Mr. Brown’s death and by the violence that followed it. He put up a sign saying proceeds from soda purchases would benefit Mr. Brown’s family. And as officials hoped for calm, so did he.

“I just want it to get back to normal,” Mr. Conner said. “Before everything happened, it was peaceful. You’d come to work, and now some people are just kind of worried that something might start up again.”