Ten years after 9/11, FBI Director Robert Mueller said the bureau had changed its traditional crime-solving approach in way that "prioritizes the collection and utilization of intelligence to develop a comprehensive threat picture, enabling strategic disruptions of terrorist networks before they act."
"This focus on the overall threat picture also elevates the need for information sharing, thereby changing the FBI's role in and relationships with both the intelligence and law enforcement communities," Mueller told a congressional committee in October 2011.
In the Tsarnaev case, the FBI investigation automatically put his name in three government terrorism-linked databases.
One was the FBI's Terrorist Screening Database (TSDB), which includes more than 500,000 names of known or suspected foreign and domestic terrorists. Another was the Terrorist Identities Datamart Environment list, known as TIDE, which is maintained by the National Counterterrorism Center.
The TIDE list is similar to the TSDB database, but contains more detailed, raw intelligence. They are linked and both are tools for law enforcement and intelligence agencies to share information on terrorism suspects.
From the lists, the FBI Terrorism Screening Center recommends which names should be put on "no-fly" watch lists and other screening tools used by the Transportation Security Administration, Customs and Border Protection, the State Department and the FBI.
But he was never on any watch list or "no fly" list, officials said.
However, it also was on a Customs and Border Protection list known as TECS, which is used to detect unusual or suspicious travel, a federal law enforcement official told CNN.
Because the FBI investigation turned up no threat and Russia never responded to requests for further information, the probe was halted, officials said.
During the investigation, the database included a notation that lasted a year that signaled authorities if Tsarnaev left the country.
Democratic Sen. Dianne Feinstein said Wednesday that the notification time period might be too short for people like Tsarnaev.
"Should the year be more? I happen to believe it should be," the California Democrat told reporters, adding that "when a Russian security bureau says we have concerns that someone has been radicalized, I would pay more attention to it."
Napolitano, meanwhile, lobbied for an immigration reform bill under consideration by Congress that she implied would have increased awareness of Tsarnaev's travels through enhanced border controls.
The proposal strengthens "the electronic use of, or electronically readable passports for travel and so forth. so that we don't have any manual entries," she said.
A day earlier, Napolitano told a congressional hearing that Tsarnaev's name was misspelled on his Aeroflot airline ticket, which caused what she called a "missed match."
However, she also said that "even with the misspelling, in our current system there are redundancies and so the system did ping when he was leaving the United States."
CNN law enforcement analyst Tom Fuentes, a former FBI official, explained what happened.
"By the time he comes back, the FBI case is closed and, again, no additional information comes back from the Russians to keep an eye on him or that he's on his way back to your country," Fuentes said. "Once the FBI case is closed, there is no further monitoring by the FBI of his activity or whether he's going to these Jihadi Web sites or becoming increasingly radicalized."
Goodlatte said his judiciary panel and others in the Republican-led House "will definitely be following through to find out what happened, and what can be done to improve on communications between homeland security, the FBI and other enforcement agencies."
White House spokesman Jay Carney called for patience.
"I think we need to let the investigation unfold and make the assessment when we know all the facts," Carney said.
Tsarnaev was an immigrant from the volatile Caucasus region of southwest Russia who had legal residence in the United States and sought last year to become fully naturalized, like his brother.
However, Homeland Security officials rejected the citizenship request due to the FBI questioning before the Russia trip.
An FBI statement Friday said a foreign government -- later identified by legislators as Russia -- asked for information on Tsarnaev "based on information that he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel to the country's region to join unspecified underground groups."
In response, the FBI said, it "checked U.S. government databases and other information to look for such things as derogatory telephone communications, possible use of online sites associated with the promotion of radical activity, associations with other persons of interest, travel history and plans, and education history."