"I think, every step of the way, and is right in the middle of this. So I think she does have information. I think she's in the sights of the FBI right now. I think they're looking at her very closely," McCaul said.

On Thursday, the Associated Press reported Russell had hired New York lawyer Joshua Dratel to represent her. Dratel has represented a number of accused terror suspects, including at least on Guantanamo detainee

Russell has not been charged with any crime, but has met repeatedly with investigators from the FBI.

McCaul also suggested Friday that Tsarnaev's parents could have been responsible for his radicalization.

"With respect to the mother, I think she radicalized him.  Uh, and the father, I think there's a reason why he has declined his trip to come back into the United States," McCaul said.