One law enforcement official said that the F.B.I. and the police were seeking “a number of people with whom we would like to speak in furtherance of the investigation.” Asked if any were suspected accomplices or co-conspirators, the official would say only that investigators were “not ready” to classify anyone yet. Another official said that investigators had not yet uncovered any indications that the men had any affiliation with an extremist group or groups.

Several officials, asked about the tradecraft employed by the two brothers identified as suspects, said that despite the devastation they are alleged to have caused at the marathon and the killing of one police officer and grievous wounding of another, their planning and tactics appeared, at least at this point, to be flawed. “They didn’t practice tradecraft,” said one official, a veteran counterterrorism investigator who has been briefed on the case. “Listen, I just don’t understand how anybody could do something like that and basically go home and expect that they wouldn’t get caught.” 

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