"So maybe it's the system failed, didn't provide the FBI with the tools, or maybe they didn't use it properly," he added. "That's why maybe we need to find out what happened."
His comments sounded similar to those made by House Intelligence Committee Chairman Mike Rogers, who defended the FBI on Sunday.
Rogers told NBC the agency "did their due diligence" but Russian authorities "stopped cooperating" when the United States sought further clarification. Rogers also said he believed Tsarnaev may have traveled overseas using an alias.
CNN law enforcement analyst Tom Fuentes, a former FBI official, said there was little the bureau could do once Russia failed to respond to its request for further details .
"If they don't give you more, then everything that can be done has been done unless you know that there should be more to the story," Fuentes said.
He detailed how the FBI employs what amounts to "triage" to deal with what he said were tens of thousands of similar inquiries a year that require some level of bureau investigation.
"If you are getting this from a hot place like Afghanistan or the tribal area of Pakistan or places where we have had specific training camps and people deployed on purpose to come and attack us, then that is the highest priority," he said. "And even there, many of the people that go back and forth are visiting family. I mean, they are not always going back to be trained to be terrorists or always going back for refresher courses on terrorism."
Regarding Russia, Fuentes noted the ongoing conflict with Chechen separatists that may have caused Moscow's request for information on Tsarnaev.
"That's been an ongoing fight, but it's been localized," he said, adding that he couldn't recall a case in which a Chechen trained at home came to attack the United States.
However, Fuentes noted that al-Qaida had sent people to the Caucasus region for training that included bomb building.
Now U.S. investigators need to find out if the Tsarnaevs "had connections, were they deployed by a bigger group, and are there other terrorists in the United States," Fuentes said.
"Are there other explosive devices hidden somewhere or booby traps created, a cache of weapons?" he wondered. "That'll be the task."