U.S. Republican lawmakers questioned Sunday whether the FBI had fumbled the case of one of the two Boston Marathon bombing suspects, saying it was one of a series in which someone the agency had investigated had gone on to participate in terrorist attacks.

House of Representatives Homeland Security Committee Chairman Michael McCaul said he wrote to the FBI and other officials asking why more wasn’t done after the FBI’s 2011 interview with Tamerlan Tsarnaev, the elder of two brothers suspected in the Boston bombing, who was killed in a shootout with U.S. police. He was 26.

“Because if he was on the radar and they let him go, he’s on the Russians’ radar, why wasn’t a flag put on him, some sort of customs flag?,” McCaul, of Texas, said on CNN’s “State of the Union” program. “And I’d like to know what intelligence Russia has on him as well.”

McCaul said he believed Tsarnaev had “received training” while on a trip to Russia last year. U.S. investigators say Tsarnaev, an ethnic Chechen, spent six months in Russia last year.

Tsarnaev’s brother Dzhokhar, 19, remained hospitalized in serious condition on Sunday, unable to speak.

Three people were killed in the bombing on Monday near the finish line of the famed marathon and 176 were injured.

McCaul’s letter, which was also signed by the former chairman of the homeland security panel, Representative Peter King of New York, said Tamerlan Tsarnaev “appears to be the fifth person since Sept. 11, 2001, to participate in terror attacks despite being under investigation by the FBI.”

They said the others were Anwar al-Awlaki, a U.S.-born cleric and leader of al Qaeda’s affiliate in Yemen who was killed in a U.S. drone strike; David Headley, an American who admitted scouting targets for a 2008 Islamic militant raid on Mumbai; Carlos Bledsoe, who killed an Army private outside a military recruiting office in Arkansas in 2009; and Nidal Hasan, who is on trial for killing 13 people at Fort Hood Texas in 2009.

In addition, Farouk Abdulmutallab, who tried to bring down a U.S. jetliner over Detroit on Christmas Day 2009, had been identified to the CIA as a potential terrorist, the letter said, adding the cases “raise the most serious questions about the efficacy of federal counterterrorism efforts.”

House Intelligence Committee Chairman Mike Rogers, a former FBI agent, defended the agency. The Michigan Republican said it had performed a “very thorough” review of the older brother in 2011, but then failed to receive further cooperation from the foreign intelligence agency that requested the review. U.S. law enforcement sources say this agency was from Russia.

“That case was closed prior to his travel, so I don’t think we missed anything,” Rogers said on NBC’s “Meet the Press.”

“At some point they (the FBI) asked, is there more clarifying information, and never received that clarifying information, and at some point they have nothing. You can’t ask them to do something with nothing,” Rogers said.

But King told “Fox News Sunday” he wondered why the FBI did not take more action after Tsarnaev returned to the United States and put statements on his website “talking about radical imams.”

“I’m wondering, again, is there something deficient here? What was wrong?” King asked.

The McCaul-King letter asked for all information the U.S. government had on Tsarnaev before April 15. It was also addressed to Director of National Intelligence James Clapper and Homeland Security Secretary Janet Napolitano.

(Reuters)