– As churches paused on Sunday to mourn the dead and console the survivors of the Boston Marathon bombing, 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 with a gunshot wound to the throat.

In addition, officials said they were increasingly certain that the two suspects had acted on their own, but were looking for any hints that someone had trained or inspired them. The FBI is broadening its global investigation in search of a motive and pressing the Russian government for more details about a Russian request to the FBI in 2011 about one of the suspect’s possible links to extremist groups, a senior U.S. official said Sunday.

The suspects in the twin bombings that killed three people and wounded more than 180 are two ethnic Chechen brothers from southern Russia — 19-year-old Dzhokhar Tsarnaev and his 26-year-old brother, Tamerlan. Their motive remained unclear.

The older brother was killed during a getaway attempt. The younger brother, Dzhokhar Tsarnaev, was captured on Friday, after he was found in a tarp-covered boat in a suburban Boston back yard. Authorities would not comment on whether he had been questioned.

New details about the suspects, their alleged plot and the expanding inquiry emerged Sunday, including the types of weapons that were used and the bomb design’s link to a terrorist manual. Lawmakers also accused the FBI of an intelligence failure, questioning whether the agency had responded forcefully enough to Russia’s warnings.

Dzhokhar Tsarnaev, 19, remained in a Boston hospital in serious condition, and authorities said they believed that he had tried to kill himself, because a gunshot wound to his neck “had the appearance of a close-range, self-inflicted style” injury, the senior U.S. official said.

More details of what the authorities said was the original plot were becoming clearer. Boston Police Commissioner Edward Davis said the authorities believed that Tsarnaev and his older brother, Tamerlan, 26, had planned more attacks beyond the bombings. When the suspects seized a vehicle and held the driver hostage, they told him that they planned to head to New York, the senior U.S. official said Sunday.

It was not clear whether the suspects told the driver what they planned to do there.

Davis told CBS News’ “Face the Nation” on Sunday: “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.”

Among the unanswered questions facing investigators are where the suspects acquired their weapons and explosives, how they got the money to pay for them and whether others helped plan and carry out the attack. Boston Mayor Thomas Menino said he believed the brothers were not affiliated with a larger network.

“All of the information that I have, they acted alone,” he said on ABC News’ “This Week.”

Some investigators said they believe the suspects used a design for the pressure-cooker bombs they allegedly detonated from a manual published in the online English-language magazine of Al-Qaida’s affiliate in Yemen. Menino said Tamerlan Tsarnaev had “brainwashed” his younger brother to follow him and “read those magazines that were published on how to create bombs, how to disrupt the general public, and things like that.”

Uncle: Suspect had changed

The suspects’ uncle, Ruslan Tsarni, who lives in Maryland, said Sunday that he had first noticed a change in the older brother in 2009. Tsarni sought advice from a family friend, who told him that Tamerlan Tsarnaev’s radicalization had begun after he met a recent convert to Islam in the Boston area. Tsarni said he had later learned from a relative that his nephew had met the convert in 2007.

As scrutiny increased on the how the brothers had been radicalized, Rep. Michael McCaul, R-Texas, who heads the Homeland Security Committee, and Rep. Peter T. King, R-N.Y., who is also on the panel, sent a letter to the directors of three of the nation’s leading intelligence-gathering agencies calling the FBI’s handling of the case “an intelligence failure.”

They said Tamerlan Tsarnaev was the fifth man since the Sept. 11, 2001, attacks to be suspected of committing terrorism while under investigation by the bureau. Agents had questioned him in 2011 in response to a request from the Russian government, a year before he traveled to Chechnya and Dagestan, predominantly Muslim republics in the North Caucasus region of Russia. Both have been hotbeds of militant separatists.

The request from the Russian government was directed to the FBI’s legal attache at the U.S. Embassy in Moscow in January 2011, a senior U.S. official said. The Russians feared Tamerlan Tsarnaev could be a risk, and said their request was “based on information that he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel to the country’s region to join unspecified underground groups,” the FBI said in a statement Friday.

A senior U.S. official said Sunday that despite requests from U.S. officials for more details at the time, this was all the information the Russians provided.

In the wake of the current furor, the FBI has pressed Russian authorities for more details about Moscow’s original request on Tamerlan, as well as any information the Russian intelligence services have developed since then, according to a senior U.S. official. These discussions are “sensitive,” the official said, because of the differences in protocol and laws between the two countries, and the Russians’ reluctance to disclose confidential intelligence to foreign governments.

Across the rattled streets of Boston, churches opened their doors on Sunday 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 attack and a Massachusetts Institute of Technology police officer slain Thursday were displayed on the altar, each face illuminated by a glowing white candle.

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.

A six-block segment of Boylston Street, where the bombs were detonated, remained closed Sunday. City officials were mapping out a plan to reopen it, but the exact timetable was uncertain.

 

The New York Times contributed to this report.