WASHINGTON – The older brother suspected in the Boston Marathon bombings had an application for U.S. citizenship placed on hold after the FBI questioned him on potential Islamic extremist ties, raising questions about whether he could have been identified before carrying out the attack.

The inquiry into why Tamerlan Tsarnaev, 26, and his brother, Dzhokhar Tsarnaev, 19, may have detonated bombs near the finish line widened in scope Sunday as the younger brother remained hospitalized.

“There are questions that have to be answered,” Sen. Charles Schumer, D-N.Y., said Sunday on CNN’s “State of the Union” program. “This man was pointed out by a foreign government to be dangerous. He was interviewed by the FBI once. What did they find out? What did they miss? Then he went to Russia and to Chechnya. Why wasn’t he interviewed when he came back?”

Tamerlan Tsarnaev was brought to the FBI’s attention two years ago by a foreign government that said he held extremist Islamist beliefs, the agency said in a statement. The FBI said it found no evidence of terrorist activity at the time.

Rep. Michael McCaul, R-Texas, chairman of the House Homeland Security Committee, said on the Sunday CNN program that “my understanding is the Russian intelligence service contacted the FBI,” which “let him go” after he was interviewed.

“I want to know how the FBI or the system dropped the ball when he was identified as a potential terrorist,” Sen. Lindsey Graham, R-S.C., said on the CNN program. “It’s people like this that you don’t want to let out of your sight and this was a mistake.”

The request to investigate Tamerlan Tsarnaev in 2011 advised that he “was a follower of radical Islam” and had “changed drastically since 2010 as he prepared” for his trip to Russia, raising fears he planned “to join unspecified underground groups,” the FBI said on its website.

The new FBI-led probe is paying close attention to a six-month trip Tamerlan Tsarnaev, an immigrant of Chechen descent, took to Russia in January 2012, said two law enforcement officials briefed on his travel. During his time there he visited Chechnya and neighboring Dagestan, both regions of Russia that have been embroiled in Islamist separatist movements.

His father told the Associated Press that his son stayed with him in Makhachkala, the capital of Dagestan, where the family lived briefly before moving to the United States a decade ago. The father had only recently returned.

“He was here, with me in Makhachkala,” Anzor Tsarnaev said in a telephone interview. “He slept until 3 p.m., and you know, I would ask him: ‘Have you come here to sleep?’ He used to go visiting, here and there. He would go to eat somewhere. Then he would come back and go to bed.”

He said his son went to the mosque for prayers, but would not have come under the influence of radical imams, who he said stay up in the mountain villages.

Despite the violence in Dagestan, Anzor Tsarnaev said Sunday that his son did not want to leave and had thoughts on how he could go into business. But the father said he encouraged him to go back to the United States and try to get citizenship. Tamerlan Tsarnaev returned to the United States in July.

His mother said that he was questioned upon arrival at New York’s airport.

“And he told me on the phone, ‘Imagine, Mama, they were asking me such interesting questions as if I were some strange and scary man: Where did you go? What did you do there?’” Zubeidat Tsarnaeva recalled her son telling her at the time.

After finishing its review of Tsarnaev in 2011 with no indication of suspicious activities, the FBI requested more information and details from the Russian intelligence service about what prompted the warning. They received no response, according to the statement.

Rep. Mike Rogers, R-Mich., a former FBI agent who is chairman of the House Intelligence committee, said he wasn’t certain there was a lapse.

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

No evidence has emerged since to link Tsarnaev to militant groups in Russia’s Caucasus. And on Sunday the Caucasus Emirate, which Russia and the United States consider a terrorist organization, denied involvement in the Boston attack.The FBI says it asked for more details from the Russian intelligence service about what prompted the warning but got no response.