A Federal Bureau of Investigation analysis of the bombs used in the Boston Marathon attacks has concluded that makers of the devices had some knowledge beyond the step-by-step recipes already described by the surviving suspect in the attack.

Dzhokhar Tsarnaev has told interrogators that he and his brother used bomb-making instructions found in Inspire, an online al Qaeda magazine, according to federal officials. His brother, Tamerlan Tsarnaev, the other accused bomber, was killed during a gunfight with police in Watertown, Mass.

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