Tsarnaev was reacting to a speaker who likened the Muslim Prophet Mohammed to Martin Luther King Jr., the board member said. He calmed after worshippers spoke with him, and returned often for pre-dawn prayers on Fridays, the board member said.
Dzhokhar Tsarnaev also sometimes attended prayers -- but only with his brother, the board member said.
Memorials and tributes
Boston officials planned a moment of silence for 2:50 p.m. Monday to mark the passing of one week since the bombings. A minute later, bells will toll to honor the victims.
One of those victims, Krystle Campbell was memorialized Monday morning in a service at St. Joseph Catholic Church in Medford, Massachusetts.
After the service, police officers lined the street in front of the church as other officers wearing dress uniforms saluted as the casket bearing her remains was taken from the church and loaded into a hearse.
Another memorial service was scheduled Monday night for victim Lingzi Lu, a student from China.
Also on Monday, runners in at least 80 cities will participate in the "Run for Boston in Your City" campaign, organizer Brian Kelley said. The global campaign is "a run for those that were unable to finish, a run for those that may never run again" and "a run for us to try and make sense of the tragedy that has forever changed something we love," according to organizers.
A week after the marathon bombings, 50 people remain hospitalized, including two in critical condition, according to a CNN tally.
At least a dozen survivors have endured amputations.
Patients at Boston Medical Center have received visits from war veterans who have also suffered amputations. The vets, Dr. Jeffrey Kalish said, told patients that their lives aren't over because they've lost limbs.
"We've seen really tremendous success and great attitudes," he said.
Also Monday, Davis -- the Boston police commissioner -- said transit system police officer Richard Donohue, wounded in the firefight with the Tsarnaev brothers, was improving.
"He was in grave condition when he went to the hospital, so we're very optimistic at this point in time, and our prayers are with him and his family," he said.
Dzhokhar Tsarnaev, meanwhile, remains in serious but stable condition, according to the U.S. Attorney's Office District of Massachusetts. A federal law enforcement source with knowledge of the investigation told CNN the younger brother has a gunshot wound to his neck, and he had a tube down his throat to help him breathe.
It's unclear whether Tsarnaev was wounded during his capture or in the earlier shootout with police that left his older brother dead, said the source, who spoke on condition of anonymity.
Getting back to normal
It could take up to two more days before the area around the site of the explosions can reopen to the public, Davis said.
The FBI has not yet turned the scene back over to local authorities, the police chief said.
"We have to allow store owners to go in there first. It won't be open to the general public for maybe another day so the store owners can get their business back on track," Davis said. "We want to get people back in their homes as soon as possible, and we're working diligently on that right now."