Classical music fans at a D.C. auditorium Sunday thought they were witnessing the arrest of a man suspected of killing a woman in Alexandria last week when, moments after a chamber concert performance, police took a bearded audience member aside for questioning.

Instead, the episode highlighted the edgy mood of the Washington region as the manhunt continues for the person who shot Ruthanne Lodato on Thursday. The November slaying of Ronald Kirby, a regional transportation planner who lived about a mile from Lodato, is also unsolved. Police are looking at any similarities in those cases and the 2003 slaying of Nancy Dunning, the wife of the late sheriff James Dunning.

According to two witnesses, applause was still ringing in the auditorium of the National Academy of Sciences building on Constitution Avenue NW when armed U.S. Park Police officers rushed down the aisle to a man seated near the front.

The witnesses, who spoke on the condition of anonymity to avoid publicity, described the man as elderly and balding, with a white beard. They had earlier noted to themselves his resemblance to a police sketch of the shooter. “He looked a little more scruffy than most people there,” one of the witnesses said. “At intermission, he stood up, and we were, like, ‘God, that looks like the guy.’ ”

Another audience member took her suspicions further, alerting building security to the man’s presence. According to a building security officer, who declined to give his name, the woman had a photo of the sketch on her phone and became frightened when she saw the bearded man two rows in front of her. “Things started twirling in her mind,” said the guard.

Composite sketch of shooting suspect (Courtesy Alexandria City Police)

Sgt. Lelani Woods, a U.S. Park Police spokeswoman, said Park Police officers were contacted by their D.C. police counterparts and sent to the concert about 4:25 p.m.

The man stood and allowed police to walk him up the aisle and out of the hall without resisting, the witnesses said, as some in the audience continued to clap for the Catalyst Quartet. The guard said police interviewed the man briefly.

“They took him in a room in the back, and then they went their separate ways,” he said.

Crystal Nosal, an Alexandria police spokeswoman, said Sunday night that police had not made an arrest in the fatal shooting of Lodato, a 59-year-old music teacher, and had no one in custody. As to why the U.S. Park Police might have questioned someone at a D.C. concert, she said she could only speculate.

“They may have interviewed him because he fit something with the composite,” she said.

A Park Police spokesman said only that the agency had assisted with an investigation at the National Academy on Sunday.

The guard said the woman who had alerted security was so shaken that she struck another car as she was leaving the concert.

Alexandria officials said in a statement Sunday night that police officers will be out Monday in the community around Ridge Road Drive, where Lodato lived, and speaking with residents. Residents were urged to lock their doors and windows at all times and to not open their doors for strangers.

Brigid Schulte and Matt Zapotosky contributed to this report.