The car had reportedly been moving erratically Monday afternoon, and a message scrawled on it appeared to refer to 9/11, witnesses said. In a time of heightened sensitivity to such things, police soon said they were investigating a suspicious vehicle, and a street near Dupont Circle in the District was evacuated.

Matthew Kopolow-McCall was at home with his family’s 16-month-old twins when law enforcement officers came to his door in the 1700 block of R Street NW and “told us we had to evacuate,” he said. Deanna Trotter, another resident of the block, was also told “we had to get out.”

A black auto parked on the block was cordoned off with yellow tape, and authorities began examining it. Rumors about what might be inside swirled around the neighborhood. Some said it contained propane tanks. Gasoline. Possibly a bomb.

Ultimately, police said the suspicious vehicle wasn’t anything to worry about. No hazardous material was found, they said. Similar events have been common for years now, and the vigilance of law enforcement may have increased since bombs were planted at the Boston Marathon in April. Although the District incident turned out to be innocuous, it gave an example of the small dramas that many such episodes create.

“I really appreciate the police taking this seriously,” said Stephanie Maltz, an advisory neighborhood commissioner for the area.

“I would rather they take this approach” than ignore something that might turn out to be a true hazard, said Maltz, who lives on the block that was evacuated.

In an interview with a reporter, Maltz praised police for “keeping everybody calm.”

Maltz did her part, according to Kopolow-McCall. When he left home, with crying toddlers without diapers, she took it upon herself to get some, he said.

That was probably not among the duties of an ANC commissioner, Kopolow-McCall said, but after he went to a friend’s home nearby, “she found us and brought us the diapers.”

Trotter said she spent three hours, from about 3:30 p.m. to 6:30 p.m., around the corner on New Hampshire Avenue NW, much of it sitting on steps. “It wasn’t difficult,” she said. “Just boring.”

She said she later glimpsed the car that had prompted the activity. “It looked as if there were a lot of blankets inside,” she said. It gave her the impression that somebody might have been living in it, she said.

She said the man linked to the car did not appear particularly threatening. “He just looked like a person I would see on the street and would say hi to.”

As the man was escorted away by police, she said, he seemed to try to address those outside the security perimeter. She said someone thought he had given the address of a Web site. But few seemed to know just what he had said.