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Republicans ask: How much did the FBI know on Boston bomber?

Republican members of Congress are questioning how the FBI conducted its investigation into suspected Boston bomber Tamerlan Tsarnaev as details emerged that th

Republican members of Congress are questioning how the FBI conducted its investigation into suspected Boston bomber Tamerlan Tsarnaev as details emerged that the 26-year-old traveled to Russia, despite being interviewed by the agency in relation to possible ties to terrorists.

Russian officials had tipped American law enforcement in 2011 that Tsarnaev, who was born in Kyrgyzstan but became a legal permanent resident of the U.S., was “prepared to leave the United States for travel to the country’s region to join unspecified underground groups.” The FBI determined after interviewing Tsarnaev and his family members that he posed no terrorist threat.

Several members of Congress have asked if the FBI should have been more thorough, as well as questioned how well federal intelligence agencies are sharing information.

“I can understand if the FBI didn’t get all the information that maybe they should’ve or maybe it wasn’t available the first time through," Republican Rep. Peter King of New York said Wednesday on msnbc. "But then, when the Department of Homeland Security knew that he was going to Russia--the older brother—apparently, it couldn’t get back to the FBI because under FBI regulations the case had been closed by then.”

FBI officials said they did not hear back from Russian investigators when they followed up for more information after the initial investigation in 2011. Tsarnaev's name was automatically entered into the Treasury Enforcement Communication System (TECS)—a low-level government watchlist—when the FBI opened its inquiry, NBC News reported.

After the FBI closed its investigation, Russian authorities sent the same request to the CIA. The CIA then consulted with the FBI and determined that no ties between Tsarnaev and terrorists had been uncovered. The FBI followed up with Russian officials a second time, but did not receive a response.

The CIA may have entered Tsarnaev's name into the Terrorist Identities Datamart Environment (TIDES) database, which is more exclusive than the TECS list. However, federal officials said having the name on the list by itself would not set off any alarms because agents receive between 30 and 40 "pings" a day. There are more than 500,000 names on the TIDES list, Reuters reported.

Tsarnaev was killed in a standoff with police last Friday. The surviving suspect, his younger brother, was charged with the bombing on Monday. He was not on authorities' radar.

Congressional Republicans demanded access to the FBI files on Tsarnaev earlier this week, saying that Tsarnaev was "the fifth person since September 11, 2001 to participate in terror attacks despite being under investigation by the FBI."

In the letter, Texas Republican Michael McCaul, who chairs the House Homeland Security Committee and congressman King listed Anwar al-Awlaki, David Headley, Carlos Bledsoe, Nidal Hasan, and Faruq Adbulmutallab, as other suspects who carried out attacks despite being under federal surveillance.

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Janet Napolitano, secretary of the Dept. of Homeland Security, said Tuesday while testifying before a Senate Judiciary Committee hearing that the system received a “ping”—or flag—when Tsarnaev left the country in 2012.

It wasn’t clear if Homeland Security had communicated Tsarnaev's whereabouts to the FBI.

“What I’d like to know is whether or not the Department of Homeland Security shared that information with the FBI and the joint terrorism taskforce,” McCaul said Wednesday on The Daily Rundown. “That possibly could have led to opening this lead investigation back up on the older brother.”

The House Committee on Homeland Security will have its next hearing on counterterrorism efforts against biological or nuclear attacks Thursday.

Federal authorities charged 19-year-old Dzhokhar Tsarnaev with the Boston bombing from his hospital bed. He told investigators Tuesday that he and his brother did not have any accomplices in the plot.

Tsarnaev, who was recovering from injuries to his head, neck, leg, and hand, told the FBI that he and his brother believed they were defending Islam in light of the U.S. wars in Iraq and Afghanistan, NBC News reported. He also that he and his 26-year-old brother learned how to make the pressure-cooker bombs online.

An investigation into the brothers' cell phones and computers led law enforcement officials to believe that "nobody else was involved" in the explosions that left three people dead and more than 200 injured last Monday.

Members of a Cambridge mosque that Tamerlan Tsarnaev had attended had asked him to not come back until he could refrain from disrupting services. The older Tsarnaev had reportedly called a speaker who had appeared to draw comparisons between Martin Luther King Jr. and the Prophet Muhammad a "kafir," or non-believer.

Yusufi Vali, a spokesman for the mosque, told NBC News that congregants were cooperating with authorities and at least three had been questioned by police.

Tamerlan Tsarnaev was shot and killed in a shootout with police early Friday morning, after the FBI released images of the two wanted men. The younger Tsarnaev escaped, prompting a manhunt that locked down Boston until late Friday when he was captured hiding out in a boat.

Dzhokhar Tsarnaev faces a potential life sentence or the death penalty for his role in the bombings.