But Sen. Lindsey Graham, R-S.C., said the FBI "told me they had no knowledge of him leaving or coming back."
Information-sharing failures between agencies prompted an overhaul of the U.S. intelligence system after the Sept. 11, 2001, terror attacks.
Meanwhile, evidence mounted that Tsarnaev had embraced a radical, anti-American strain of Islam. Family members blamed the influence of a Muslim convert, known only to the family as Misha, for steering him toward a strict type of Islam.
"Somehow, he just took his brain," said Tamerlan's uncle, Ruslan Tsarni of Montgomery Village, Md., who recalled conversations with Tamerlan's worried father about Misha's influence.
Authorities don't believe Tsarnaev or his brother had links to terror groups. However, two U.S. officials said that Tsarnaev frequently looked at extremist websites, including Inspire magazine, an English-language online publication produced by al-Qaida's Yemen affiliate. The magazine has endorsed lone-wolf terror attacks.
Both officials spoke on condition of anonymity because they were not authorized to discuss the investigation publicly.
Eight-year-old Martin Richard, a Boston schoolboy and the youngest of those killed by the blasts, was laid to rest Tuesday after a family-only funeral Mass.
"The outpouring of love and support over the last week has been tremendous," the family said in a statement. "This has been the most difficult week of our lives."
The Richards family said they would hold a public memorial service for Martin in the coming weeks.
Dzhokhar Tsarnaev's condition was upgraded from serious to fair Tuesday as investigators continued building their case against him.
He could face the death penalty after being charged Monday with joining forces with his brother in setting off shrapnel-packed pressure-cooker bombs. Three people were killed and over 260 injured. About 50 were still hospitalized.