As churches paused to mourn the dead and console the survivors of the Boston Marathon bombing Sunday, the city's police commissioner said the two suspects had such a large cache of weapons that they were probably planning other attacks.
The surviving suspect remained hospitalized and unable to speak with a gunshot wound to the throat.
After the two brothers suspected in the attack engaged in a gun battle with police early Friday, authorities found many unexploded homemade bombs at the scene, along with more than 250 rounds of ammunition.
Boston Police Commissioner Ed Davis said the stockpile was "as dangerous as it gets in urban policing."
"We have reason to believe, based upon the evidence that was found at that scene - the explosions, the explosive ordnance that was unexploded and the firepower that they had - that they were going to attack other individuals. That's my belief at this point." Davis told CBS television's Face the Nation.
On "Fox News Sunday," he said authorities cannot be positive there are not more explosives somewhere that have not been found. But the people of Boston are safe, he insisted.
The suspects in Monday's twin bombings at the marathon finish line that killed three people and wounded more than 180 others are two ethnic Chechen brothers from southern Russia who had been in the US for about a decade - 19-year-old Dzhokhar Tsarnaev and his 26-year-old brother, Tamerlan. Their motive remained unclear.
The older brother was killed in the gun battle during a getaway attempt. The younger brother, Dzhokhar Tsarnaev, was still in serious condition Sunday after his capture Friday from a tarp-covered boat in a suburban Boston backyard. Authorities would not comment on whether he had been questioned.
Sen. Dan Coats of Indiana, a member of the Senate Intelligence Committee, said Tsarnaev's throat wound raised questions about when he will be able to talk again, if ever.
The wound "doesn't mean he can't communicate, but right now I think he's in a condition where we can't get any information from him at all," Coats told ABC's This Week.
It was not clear whether Tsarnaev was shot by police or inflicted the wound himself.
In the final standoff with police, shots were fired from the boat, but investigators have not determined where the gunfire was aimed, Davis said.
The younger Tsarnaev who is hospitalized at Boston's Beth Israel Deaconess Medical Center could be charged any day.
The most serious charge available to federal prosecutors would be the use of a weapon of mass destruction to kill people, which carries a possible death sentence. Massachusetts does not have the death penalty.
US officials said an elite interrogation team would question Tsarnaev, a Massachusetts college student, without reading him his Miranda rights, which guarantees the right to remain silent and the right to an attorney.
Such an exception is allowed on a limited basis when the public may be in immediate danger, such as instances in which bombs are planted and ready to go off.
The federal public defender's office in Massachusetts said it has agreed to represent Tsarnaev once he is charged.
In an interview with The Associated Press, the parents of Tamerlan Tsarnaev insisted Sunday that he came to Dagestan and Chechnya from January to July last year to visit relatives and had nothing to do with the Islamic militants operating in this volatile region in southern Russia.
His father said his son slept much of the time.
When the two ethnic Chechen suspects were identified, the FBI said it reviewed its records and found that in early 2011, a foreign government - which law enforcement officials confirmed was Russia - had asked for information about Tamerlan Tsarnaev.
The FBI said it was told that Tsarnaev was a "follower of radical Islam" and was preparing to travel to this foreign country to join unspecified underground groups.
The FBI said that it responded by interviewing Tsarnaev and family members, but found no terrorism activity.
No evidence has emerged since to link Tsarnaev to militant groups in Russia's Caucasus.
And on Sunday the Caucasus Emirate, which Russia and the US consider a terrorist organization, denied involvement in the Boston attack.
Chechnya has been the scene of two wars between Russian forces and separatists since 1994. That spawned an Islamic insurgency that has spread throughout Russia's Caucasus, with the worst of the violence now in Dagestan.
Despite the violence in Dagestan, Anzor Tsarnaev said Sunday that his son did not want to leave and had thoughts on how he could go into business. But the father said he encouraged him to go back to the United States and try to get citizenship.
Investigators have not offered a motive for the Boston attack. But in interviews with officials and those who knew the Tsarnaevs, a picture has emerged of the older brother as someone embittered toward the US, increasingly vehement in his Muslim faith and influential over his younger brother.
Across the rattled streets of Boston, churches opened their doors to remember the dead and ease the grief of the living.
At the Cathedral of the Holy Cross in South Boston, photographs of the three people killed in the marathon attack, including a 23-year-old Chinese student, and a Massachusetts Institute of Technology police officer slain Thursday were displayed on the altar, each face illuminated by a glowing white pillar candle.
"I hope we can all heal and move forward," said Kelly McKernan, who was crying as she left the service.
obviously, the Mass today was a first step for us in that direction."
A six-block segment of Boylston Street, where the bombs were detonated, remained closed Sunday. But city officials were mapping out a plan to reopen it.
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, Massachusetts, 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 a 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 2:50pm, 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.