Investigators have always wondered if more people were involved in the bombings than just the brothers . The FBI has been investigating whether there was a broader plot to attack U.S. targets and is looking into possible connections between Tsarnaev and other Islamic extremists who may be planning attacks on American soil. : I think `` they had somebody who was more of a skilled bomb maker .. assist them '' There was no evidence the brothers ever tested their bombs before using them , CNN analyst says .
Investigators have always wondered if more people were involved in the bombings than just the brothers . Former Navy investigator : I think `` they had somebody who was more of a skilled bomb maker .. assist them '' There was no evidence the brothers ever tested their bombs before using them , CNN analyst says .