The picture emerging was of an American counterterrorism bureaucracy that stored information on the suspect, Tamerlan Tsarnaev, but never found reason to investigate after an initial review by the F.B.I., requested by the Russia government, found no information that tied him to extremist groups.
The Central Intelligence Agency replied to a request from Russia's intelligence service in September 2011 that it had no derogatory information about Mr. Tsarnaev, but asked the main United States counterterrorism agency to add his name to a watch list, an American intelligence official said Wednesday.
That database, the Terrorist Identities Datamart Environment, or TIDE, is the main database from which other government watch lists are drawn, including the F.B.I.'s Terrorist Screening Database and the Transportation Security Administration's "no-fly" list.
Six months before the request to the C.I.A., the Russians had made a similar request of the F.B.I., claiming Mr. Tsarnaev "was a follower of radical Islam and a strong believer," according to a statement released last week by the F.B.I. The bureau reviewed criminal data bases and interviewed Mr. Tsarnaev and family members, and found no information that tied him to militants.
In closing out its report, the F.B.I.'s field office in Boston added Mr. Tsarnaev's name to a second watch list, the Treasury Enforcement Communications System, that was set up to send an electronic message to United States customs officials when Mr. Tsarnaev left the country.
When Mr. Tsarnaev left on Jan. 12, 2012, for a six-month trip Dagestan and Chechnya, predominantly Muslim republics in the North Caucasus region of Russia, his flight reservation set off a security alert to customs authorities when he departed, the homeland security secretary, Janet Napolitano, told a Senate committee on Tuesday.
But Mr. Tsarnaev's departure did not trigger a similar alert on the TIDE watch list because the spelling variants of his name and birthdates entered into the system – exactly how the Russian government had provided the data months earlier – were different enough from the correct information to prevent an alert, a United States official said.
When Mr. Tsarnaev returned in July last year, the travel alert "at that point was more than a year old and had expired," Ms. Napolitano said.
The F.B.I. initially received a one-page request from the Russian government in March 2011 that stated Mr. Tsarnaev "had changed drastically since 2010," and was preparing to travel to a part of Russia "to join unspecified underground groups."
In June 2011, the F.B.I. concluded that it could not find any connections to extremists and in August provided its results to the Russians, according to the official. When the F.B.I. provided the results to the Russians, it requested additional information on Mr. Tsarnaev and also asked to be informed of any further developments.
Shortly thereafter, the F.B.I. reiterated its request to the Russians for more information. The Russians, however, did not respond with anything new. A month later, the Russians sent the same request for a check on Mr. Tsarnaev to the C.I.A.
That prompted the C.I.A.'s review, which came to a similar conclusion as the F.B.I's. Around that time, the F.B.I. learned of the request to the C.I.A. and went back to the Russians once again to see if they had additional information on Mr. Tsarnaev, according to the official.
The official said the Russians never provided additional information.
