The suspect wearing a white ball cap -- identified as "suspect number two" -- was observed in a video dropping a backpack at the location of one of the bombings.
The FBI asks anyone with knowledge of either suspect to call 1-800-CALL-FBI (1-800-225-5324).
Reddit user streetsim snapped a photo he says is of Suspect 1, which matches the back of the Bridgestone Golf cap he appears to be wearing:
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