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Republican senators demand hearings on Boston Marathon

Two Republican senators are demanding congressional hearings to examine whether U.S. intelligence officials could have prevented the attacks on the Boston Marathon.

Sens. John McCain, R-Ariz., and Kelly Ayotte, R-N.H., want the Senate Homeland Security Committee to find out if government agencies were able to communicate with each other sufficiently -- and if they didn't, whether properly sharing that information could have alerted authorities to Tamerlan Tsarnaev and possibly saved lives.

"We are requesting that the Homeland Security and Governmental Affairs Committee hold a hearing as soon as possible to investigate whether our intelligence officials had information that could have prevented these attacks," McCain and Ayotte wrote Wednesday in a letter to Sen. Thomas Carper, D-Del, the committee's chairman.

"It does not appear that the money spent or the information sharing environment put into place after 9/11 were useful in apprehending the Tsarnaev brothers, specifically Tamerlan Tsarnaev," the two wrote.

The call for hearings is the latest escalation of an increasingly politicized conversation on Capitol Hill about the bombings that killed three people and injured scores more. 

Lawmakers are still in the early phases of learning exactly what the U.S. government knew about Tamerlan Tsarnaev, the now-deceased older brother of living suspect Dzhokhar Tsarnaev, and how the government's various security agencies handled and shared that information. Both the Senate and House Intelligence Committees have been briefed by security officials, and the Senate will have a classified briefing for all members of the upper chamber on Thursday.

But it's already clear that lawmakers are seizing on possible mistakes the government made in the course of tracking Tamerlan Tsarnaev after the Russian government asked the FBI and the Central Intelligence Agency for more information about him in separate requests. 

A central issue is the trip Tamerlan Tsarnaev took to Russia in 2011. U.S. agencies had asked the Russian government for more information about him, but hadn't received a response. Tamerlan's trip abroad did trigger an alert, law enforcement officials have said, because he had been placed into a preliminary database the intelligence community uses. 

But federal officials didn't keep tabs on him during his trip to Russia or after he returned to the U.S.

That reality drew some scrutiny on the other side of Capitol Hill, where the House Intelligence Committee received a classified briefing Wednesday afternoon with officials from the FBI, National Counterterrorism Center and Department of Homeland Security.

"I think it's important that we continue to do more in Russia, to find out when the older brother went to Russia, who did he contact? Was he radicalized there? We need more information from that," said Democratic Rep. Dutch Ruppersberger of Maryland, the committee's ranking member.

"There was an instance where we're going to have to do some more follow up -- that does appear that somebody made a mistake," said  Michigan Republican Rep. Mike Rogers, the committee's chairman, when asked about Tamerlan Tsarnaev's trip back to the U.S. from Russia.

Rogers, when pressed, declined to say which government agency he thought made the mistake.

Rogers emphasized, though, that the FBI had found no "derogatory information" -- red flags -- about Tsarnaev when they checked into him, which Rogers says explains why the government didn't -- or couldn't -- follow up. 

"You've got to go with what they knew at the time," Rogers said. "What they knew at the time was there was no derogatory information." 

NBC's Frank Thorp contributed to this report.