BOSTON - 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.

A mother holds the hands of her son as they attend an interfaith worship service at a memorial on Boylston Street for the victims of the Boston Marathon bombings in Boston, Massachusetts, April 21, 2013. [Photo/Agencies]

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 for there may have 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.

An aerial infrared image shows the outline of Dzhokhar Tsarnaev in a boat during the manhunt in Watertown, Massachusetts, April 19, 2013, courtesy of the Massachusetts State Police. [Photo/Agencies]

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.