Both the CIA and the FBI flagged the deceased Boston bombing suspect over possible terror ties, but he slipped through the fingers of investigators, officials have said.
The revelations have raised fresh questions over why US authorities did not further investigate Tamerlan Tsarnaev, who was killed during a shoot-out with police last week, and in doing so possibly prevent the attacks.
The CIA asked the top US counterterrorism agency to add Tsarnaev to a terror watch list more than a year before the bombings, a US intelligence official said. The spy agency made the move after Russian officials contacted their CIA counterparts in September 2011 to relay their concerns over Tsarnaev.
His younger brother, Dzhokhar, 19, has been charged with federal terror offences including the use of a weapon of mass destruction in the twin blasts on Monday last week that killed three people and wounded 264 at the Boston Marathon's finishing line.
Because the older Tsarnaev was a legal permanent US resident, the CIA then shared the information with the appropriate federal departments and agencies, telling them that he may be "of interest" to them, a US intelligence official said.
The data from Russia's Federal Security Service was "nearly identical" to information the FBI received six months earlier in March 2011, the official added.
It included two possible dates of birth, his name in Cyrillic letters and a possible variant of his name. But a review of his activities turned up nothing deemed actionable.
"No information was incorrectly entered in the watch listing system, and all the information was shared precisely as the foreign government provided it," the official said.
Tsarnaev's name was added to the Terrorist Identities Datamart Environment (TIDE), although it was unclear which agency placed it there. The National Counterterrorism Centre maintains TIDE, the main US terror database.
The database feeds information to several government watch lists, including the FBI's main Terrorist Screening Database and the "no-fly" list of the Transportation Security Administration.
The FBI's previous review of Tsarnaev had prompted his addition to a separate database.
The CIA shared the data with the National Counterterrorism Centre, Department of Homeland Security, State Department and FBI for watch-listing.