Police believe Tamerlan and Dzhokhar Tsarnaev were specially trained to carry out the devastating attack.
More than 1,000 FBI operatives were last night working to track down the cell and arrested a man and two women 60 miles from Boston in the hours before Dzhokhar’s dramatic capture after a bloody shootout on Friday.
A source close to the investigation said: “We have no doubt the brothers were not acting alone. The devices used to detonate the two bombs were highly sophisticated and not the kind of thing people learn from Google.
“They were too advanced. Someone gave the brothers the skills and it is now our job to find out just who they were. Agents think the sleeper cell has up to a dozen members and has been waiting several years for their day to come.”
A specialist team of CIA and FBI interrogators was yesterday flown to a Boston hospital to grill wounded Dzhokhar, 19, about the secret group. The University of Massachusetts student was caught on Friday after hiding out in a boat parked in a garden in locked down Watertown the day after a gun battle with police left his 26-year-old brother and a rookie cop dead.