Rep. Dutch Ruppersberger (D-Md.) told ABC News on Sunday that the FBI is investigating "persons of interest" inside the United States connected to the Boston bombing.

"There are persons of interest in the United States," said Ruppersberger, the ranking Democrat on the House Intelligence Committee. "We're looking at phone calls before and after the bombing, this type of investigation."

House Intelligence Committee Chairman Mike Rogers (R-Mich.) added, "There are still persons of interest in the United States that the FBI would like to have conversations with." But "the big unknown," he said, was the six months Tamerlan Tsarnaev spent in Russia.