However, the FBI did not know of Tamerlan Tsarnaev's trip to a region of Russia dominated by Islamist violence, The Hill reported, because an airline misspelled his name on a flight manifesto given to the U.S. government.
Napolitano told Senate Republicans her department was aware of Tamerlan Tsarnaev's departure from the country, but the FBI had closed its investigation of him when he returned, The Hill reported.
"Yes, the system pinged when he was leaving the United States. By the time he returned, all investigations -- the matter had been closed," Napolitano said.
Tamerlan Tsarnaev, 26, who with his younger brother is suspected in the Boston Marathon bombings, was killed during a shootout with police Friday. Officials have suggested he may have died because his younger brother ran over him with a vehicle as he was escaping, Dzhokhar, 19.
Tamerlan Tsarnaev, a legal U.S. resident, left the country a few months after the FBI interviewed him at the request of the Russian government to see if he had ties to radical Islamist groups.
Meanwhile, the carjacking victim of the Boston Marathon bombing suspects has opened up the possibility the pair was planning a New York City attack, investigators said.
The investigators told CBS news the cache of weapons the brothers allegedly amassed hints at plans for another attack and the brothers may have planned to go to New York.
The carjacking victim speaks little or no English but he was able to recognize certain words as the brothers conversed first in English and then in Russian.
One of the words he recognized was "Manhattan," investigators told CBS.
That resulted in a search of all Amtrak trains from Boston to New York last week and prompted New York to turn on its network of license plate readers at all bridges and tunnels coming into the city.
Surviving brother Dzhokhar Tsarnaev continued to answer questions in writing from his hospital bed Monday night.
Tsarnaev blamed his dead older brother for being behind the deadly bomb attacks, a U.S. government source told CNN.
Tsarnaev, charged Monday with using a weapon of mass destruction that resulted in three deaths and more than 260 injuries, also said he and his brother were not involved with any international terror groups, the network reported.
Earlier reports said 170 people had been injured.
Nick Martin, a spokesman for the Boston Public Health Commission, said the new figures were based on data from 25 area hospitals.
"A lot of people were injured in the blasts, but didn't think it was serious at the time," Martin told The Boston Herald. "But when their symptoms didn't go away a day or two later, they decided to have a medical professional check them out.
The New York Times separately quoted law enforcement officials as saying Dzhokhar Tsarnaev, still laying badly wounded in a Boston hospital bed, admitted he helped place the bombs.
The newspaper said he also told investigators he and his brother acted alone and said he knew of no other plots and no other bombs that had not been detonated.
The early interviews with Tsarnaev indicated the two brothers fit the profile of self-radicalized jihadis, the government source told CNN.
The younger brother told investigators his brother wanted to defend Islam from attack, CNN quoted its source as saying.
The charges were conveyed to Tsarnaev in his hospital room in the intensive care ward of Beth Israel Deaconess Medical Center, where he is recovering from multiple gunshot wounds.
His bedside initial court appearance was conducted by U.S. Magistrate Marianne B. Bowler.
Tsarnaev was able to respond to inquiries, nodding yes and at one point saying, "No," a transcript of the hearing indicated.
At the end of the session, Bowler said: "At this time, at the conclusion of the initial appearance, I find that the defendant is alert, mentally competent and lucid. He is aware of the nature of the proceedings."
If convicted, Tsarnaev faces a possible death sentence or life in prison.
His next hearing was set for May 30, court officials said.
His public defender had no immediate comment.