Investigators believe that two brothers suspected in the Boston Marathon bombing were likely planning other attacks based on the cache of weapons uncovered, the city's police commissioner has said.

As Boston-area residents came together in prayer and reflection on Sunday after a tumultuous week, the lone surviving suspect in the bombing lay hospitalised under heavy guard.

An interfaith service was held near the finish line where people set up a make-shift memorial as police cleared away debris from the bombing that killed three people and wounded more than 160.

Ed Davis, the Boston Police Commissioner, told broadcaster CBS' "Face the Nation" programme that authorities found an arsenal of homemade explosives after Friday's gun battle between police and the two suspects.

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. Ed Davis

Boston Police Commissioner,

"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," Davis said.

"That's my belief at this point."

One improvised explosive device was found in the Mercedes the brothers are accused of carjacking, he said.

The US Federal Bureau of Investigation (FBI) still was unable to interview 19-year-old Dzhokhar Tsarnaev, who remained in serious condition two days after being pulled bloody and wounded from a tarp-covered boat in a Watertown backyard.

The capture came at the end of a tense Friday that began with his 26-year-old brother, Tamerlan, dying in a gun battle with police.

Unanswered questions



Al Jazeera's Alan Fisher, reporting from Boston, said Tsarnaev was in a stable condition at Beth Israel Deaconess Medical Centre in Boston.

"We know he lost a lot of blood," Fisher said.

There was no immediate word on when Tsarnaev might be charged and what those charges would be for the attack.

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.

Family defends Tsarnaev brothers

US officials said the 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.

Miriam Conrad, public defender for Massachusetts, said he should have a lawyer appointed as soon as possible because there are "serious issues regarding possible interrogation".

Barack Obama, the US president, said there are many unanswered questions about the bombing, including whether the Tsarnaev brothers - ethnic Chechens from southern Russia - had help from others.

The president urged people not to rush judgement about their motivations.