BOSTON (AP) — Sixteen hours after investigators began interrogating him, the surviving suspect in the Boston Marathon bombings went silent: he'd just been read his constitutional rights.

Dzhokhar Tsarnaev immediately stopped talking after a magistrate judge and a representative from the U.S. Attorney's office entered his hospital room and gave him his Miranda warning, according to four officials of both political parties briefed on the interrogation. They insisted on anonymity because the briefing was private.

Before being advised of his rights, the 19-year-old suspect told authorities that his older brother, Tamerlan Tsarnaev, 26, only recently had recruited him to be part of the attack that detonated pressure-cooker bombs at the marathon finish line, two U.S. officials said.

The CIA, however, had named Tamerlan to a terrorist database 18 months ago, said officials close to the investigation who spoke to The Associated Press on condition of anonymity because they were not authorized to discuss the case with reporters.

The new disclosure that Tamerlan Tsarnaev was included within a huge, classified database of known and suspected terrorists before the attacks was expected to drive congressional inquiries in coming weeks about whether the Obama administration adequately investigated tips from Russia that Tsarnaev had posed a security threat.

Shortly after the bombings, U.S. officials said the intelligence community had no information about threats to the marathon before the April 15 explosions that killed three people and injured more than 260.

Tsarnaev died Friday in a police shootout hours before Dzhokhar was discovered hiding in a boat in a suburban back yard. He was wounded.

Washington is piecing together what happened and whether there were any unconnected dots buried in U.S. government files that, if connected, could have prevented the bombings.

Lawmakers who were briefed by the FBI said they have more questions than answers about the investigation of Tamerlan Tsarnaev. House Judiciary Chairman Bob Goodlatte, R-Va., said lawmakers intend to pursue whether there was a breakdown in information-sharing, though Rep. Adam Schiff, a California Democrat who sits on the House Intelligence Committee, said he "hasn't seen any red flags thus far."

U.S. officials were expected to brief the Senate on the investigation Thursday. That same day, the suspects' parents, Anzor Tsarnaev and Zubeidat Tsarnaeva, plan to fly to the U.S. from Russia, the father was quoted as telling the Russian state news agency RIA Novosti. The family has said it wants to take Tamerlan's body back to Russia.

It is unclear whether the issue of their younger son's constitutional rights will matter since the FBI say he confessed to a witness. U.S. officials also said Wednesday that physical evidence, including a 9 mm handgun and pieces of a remote-control device commonly used in toys, was recovered from the bombing scene.

But the debate over whether suspected terrorists should be read their Miranda rights has become a major sticking point in the debate over how best to fight terrorism. Many Republicans, in particular, believe Miranda warnings are designed to build court cases, and only hinder intelligence gathering.

Christina DiIorio Sterling, a spokeswoman for U.S. Attorney Carmen Ortiz, said in an email late Wednesday, "This remains an ongoing investigation and we don't have any further comment."

Investigators have said the brothers appeared to have been radicalized through jihadist materials on the Internet and have found no evidence tying them to a terrorist group.

U.S. investigators traveled to the predominantly Muslim province of Dagestan in Russia and were in contact with the brothers' parents, hoping to gain more information.

They are looking into whether Tamerlan, who spent six months in Russia's turbulent Caucasus region in 2012, was influenced by the religious extremists who have waged an insurgency against Russian forces in the area for years. The brothers have roots in Dagestan and neighboring Chechnya but had lived in the U.S. for about a decade.

Dzhokhar told the FBI that they were angry about the U.S. wars in Afghanistan and Iraq and the killing of Muslims there, officials said.

Dzhokhar's public defender had no comment on the matter Wednesday. His father has called him a "true angel," and an aunt has insisted he's not guilty.

Investigators have found pieces of remote-control equipment among the debris and were analyzing them, officials said. One official described the detonator as "close-controlled," meaning it had to be triggered within several blocks of the bombs.

That evidence could be key to the court case. And an FBI affidavit said one of the brothers told a carjacking victim during their getaway attempt, "Did you hear about the Boston explosion? I did that."

Officials also recovered a 9 mm handgun believed to have been used by Tamerlan from the site of an April 18 gunbattle that injured a Massachusetts Bay Transportation Authority officer, two U.S. officials said.

The officials told the AP that no gun was found in the boat where Dzhokhar was hiding. Boston police Commissioner Ed Davis said earlier that shots were fired from inside the boat.

Asked whether the suspect had a gun in the boat, Davis said, "I'm not going to talk about that."

But Kurt Schwartz, director of the Massachusetts Emergency Management Agency, said a police officer was shot within half a mile of where Tsarnaev was captured, "and I know who shot him."

Authorities had previously said Dzhokhar exchanged gunfire with them for more than an hour Friday night before they captured him inside a tarp-covered boat in a suburban Boston neighborhood backyard. But two U.S. officials said Wednesday that he was unarmed when captured, raising questions about the gunfire and how he was injured.

In other developments:

— Vice President Joe Biden condemned the bombing suspects as "two twisted, perverted, cowardly, knockoff jihadis" while speaking at a memorial service Wednesday for Sean Collier, a campus police officer at the Massachusetts Institute of Technology who was ambushed in his cruiser three days after the bombing. More than 4,000 mourners paid tribute to the officer.

— The Office of Health and Human Services in Massachusetts confirmed a Boston Herald report Wednesday that Tamerlan, his wife and toddler daughter had received welfare benefits up until last year, when he became ineligible based on family income. The state also says Tamerlan and his brother received welfare benefits as children through their parents while the family lived in Massachusetts.

— The area around the marathon finish line was reopened to the public.

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