Federal intelligence officials are looking at whether more could have been done to prevent the Boston Marathon attacks, President Barack Obama said Tuesday.
"Based on what I can see so far, the FBI performed its duties. The Department of Homeland Security did what it was supposed to be doing," Obama said. "But this is hard stuff."
The president called the review by the Director of National Intelligence's office "standard procedure," but it comes amid withering criticism from some lawmakers of how well law enforcement, intelligence analysts and the administration handled a 2011 request by Russian officials to investigate one of the two bombing suspects, Tamerlan Tsarnaev.
That year, Russian authorities alerted the United States to concerns that Tsarnaev was becoming increasingly radical. The Russians also raised questions about Tsarnaev's mother, Zubeidat Tsarnaev, according to several sources.
But the FBI found no evidence of extremist activity and closed the case. The names of both Tsarnaev and his mother were placed in a terror database, however.
Still, Tsarnaev was allowed to travel the next year to a restive Russian region rife with Islamist terror groups, and he returned to the United States after six mysterious months abroad.
Investigators have said they are looking at possible links between Tsarnaev and those groups during his time in the region.
In the days following the attacks, Republican Sen. Lindsey Graham of South Carolina led criticism of the administration's handling of the Russian reports -- questioning whether intelligence and law enforcement agencies had properly shared information that could have prevented the April 15 bombings.
Three people died in the attack and more than 260 were wounded. Authorities say Tamerlan Tsarnaev and his younger brother, Dzhokhar, also killed a police officer. Twenty people remained hospitalized Tuesday, according to a CNN tally.
"I just find it really unnerving that we could have had him in FBI custody in 2011 and did a whole profile of him, and after the attack that his name did not surface, that we didn't check the database or the database had him missing," Graham said at the time of the older Tsarnaev.
Obama rejected Graham's criticisms Tuesday, saying "it's not as if the FBI did nothing."
"They not only investigated the older brother, they interviewed the older brother," the president said. "They concluded that there were no signs that he was engaging in extremist activity."
Obama said the intelligence review, while not prompted by the criticisms, would "leave no stone unturned."
"We want to see, is there in fact additional protocols and procedures that could be put in place that would further improve and enhance our ability to detect a potential attack," he said.
Graham responded sharply to Obama after the news conference, saying the Boston bombing joins the earlier attack on the U.S. consulate in Benghazi, Libya, as evidence of administration failures. Four Americans, including U.S. Ambassador Christopher Stevens, died in the Libya attack.
"In Benghazi, multiple requests for increased security were denied and numerous warnings from Ambassador Stevens about the growing threats from al Qaeda were ignored by Washington," Graham said.
"In Boston, both the FBI and CIA were warned by the Russians about a radical Islamist in our midst. Once enrolled in the system as a potential terror suspect, the older brother was able to travel back to Russia unimpeded by (the Department of Homeland Security) or any of our intelligence agencies. Agencies under your control were unable to coordinate the information they received on the Boston terrorists.
"If Benghazi is not an example of system failure before, during and after the attack, what would be? If Boston is not an example of a pre-9/11 stovepiping mentality, what would be?" Graham asked.
Over the weekend, news emerged that Russian authorities had intercepted a phone call in early 2011 from one of the Tsarnaev brothers in the United States to their mother in Dagestan. The call included a vague discussion of jihad, an official with knowledge of the investigation told CNN.
That information didn't make its way to the FBI before the bombings, the official said.
Last week, Russian President Vladimir Putin said he had regrets that Russian intelligence wasn't able to provide more information to U.S. officials before the bombing, and said he hoped the incident would spark greater cooperation between U.S. and Russian counterterrorism officials.
Russia has been "very cooperative with us since the Boston bombing," Obama said Tuesday.
"Obviously, old habits die hard," he said. "There's still suspicions sometimes between our intelligence and law enforcement agencies that date back in some cases 10, 20, 30 years, to the Cold War."
Amid the political acrimony, the painstaking work of building a criminal case against the surviving terror suspect went on.
While the elder Tsarnaev died April 19 after a firefight with police, his 19-year-old brother Dzhokhar is being held at a federal Bureau of Prisons medical center in Devens, Massachusetts, on a charge of using a weapon of mass destruction. He faces a possible death penalty if convicted.
On Monday, a federal judge appointed prominent defense lawyer Judy Clarke to represent him.
Clarke has represented Ted Kaczynski, the Unabomber; Eric Rudolph, the 1996 Atlanta Olympics bomber, and Jared Lee Loughner, who pleaded guilty in the Tucson, Arizona, shooting that killed six and left then-U.S. Rep. Gabrielle Giffords seriously wounded.
Very preliminary talks
Federal prosecutors and the defense team of Dzhokhar Tsarnaev have had some very preliminary talks over the "past few days" to potentially allow the surviving suspect to resume providing information to investigators, possibly in exchange for eliminating the possibility of a death penalty if he is convicted, two government sources told CNN on Tuesday.
The communications are in the very early stages, and not a sign lawyers for either side is ready to make a deal, said one source, who did not want to be identified because of the sensitive nature of the private discussions. The source stressed these are not formal talks -- with a U.S. Justice Department official saying it would not be accurate to refer to the conversations as negotiations.
Prosecutors have not said they will definitely seek the death penalty in the case, but it is an option under the federal law the 19-year-old is accused of violating. Attorney General Eric Holder would have the final say.
These kinds of conversations are not unusual in such high-profile cases, legal sources say.
Monday, news emerged that federal agents are looking into possible links between Tamerlan Tsarnaev and a Canadian jihadist killed by Russian troops in 2012, a source being briefed on the investigation said.
William Plotnikov and six others died in a firefight with Russian forces in the southwestern republic of Dagestan in July 2012 -- while Tsarnaev was visiting the region, the source said. The 23-year-old Plotnikov was born in Russia, but his family moved to Canada when he was a teenager.
Tsarnaev flew out of Dagestan two days after Plotnikov's body was prepared for burial, according to the source. Investigators are looking into the possibility he left