Mayor Thomas Menino said Sunday that once the scene is released by the FBI, the city will follow a five-step process, including environmental testing and a safety assessment of buildings. The exact timetable was uncertain.
Boston's historic Trinity Church could not host services Sunday because it was within the crime scene, but the congregation was invited to worship at the Temple Israel synagogue instead. The FBI allowed church officials a half-hour Saturday to go inside to gather the priests' robes, the wine and bread for Sunday's service.
Trinity's Rev. Samuel T. Lloyd III offered a prayer for those who were slain "and for those who must rebuild their lives without the legs that they ran and walked on last week."
"So where is God when the terrorists do their work?" Lloyd asked. "God is there, holding us and sustaining us. God is in the pain the victims are suffering, and the healing that will go on. God is with us as we try still to build a just world, a world where there will not be terrorists doing their terrible damage."
Near the crime scene, Dan and Keri Arone were pushing their 11-week-old daughter in a stroller when they stopped along Newbury Street, a block from the bombing site, to watch investigators in white jumpsuits scour the pavement. Wearing his bright blue marathon jacket, Dan Arone said he had crossed the finish line 40 minutes before the explosions.
The Waltham, Mass., couple visited the area to leave behind pairs of their running shoes among the bouquets of flowers, hand-written signs and other gifts at a makeshift memorial on Boylston Street, near the police barriers.
"I thought maybe we'd somehow get some closure," Dan Arone said of leaving behind the sneakers. "But I don't feel any closure yet."
The federal Bureau of Alcohol, Tobacco, Firearms and Explosives was tracing the suspects' weapons to try to determine how they were obtained.
Neither of the brothers had permission to carry a gun. Cambridge Police Commissioner Robert Haas said it was unclear whether either of them ever applied for a gun permit, and the applications are not considered public records.
But the younger brother would have been denied a permit based on his age alone. Only people 21 or older are allowed gun licenses in Massachusetts.
Meanwhile, surgeons at a Cambridge hospital said the Boston transit police officer wounded in a shootout with the suspects had lost nearly all his blood, and his heart had stopped from a single gunshot wound that severed three major blood vessels in his right thigh.
Richard Donohue, 33, was in critical but stable condition. He is sedated and on a breathing machine but opened his eyes, moved his hands and feet and squeezed his wife's hand Sunday.
Massachusetts Gov. Deval Patrick is asking residents to observe a moment of silence Monday at the time the first of two bombs exploded. The one-minute tribute is scheduled for 2:50 p.m., exactly a week after the attacks. It will be followed by the ringing of bells in Boston and elsewhere in Massachusetts.
In New York, thousands of runners donned "I Run for Boston" bibs during a 4-mile run in Central Park, one of a number of races held around the world in support of the victims of the marathon bombings.
Across the Atlantic Ocean, thousands of London Marathon runners offered their own tributes. The race began after a moment of silence, and many competitors wore black armbands as a sign of solidarity.
Associated Press writers Meghan Barr and Michael Hill in Boston and Michelle R. Smith in Providence, R.I., contributed to this report.