[Ray76]

What about the two identically outfitted guys in khaki? Same pants, same black jacket, same black pack, together. These guys are pros. Who? Why?

[MHGinTN]

ex military. Part of a firm hired probably to be on alert for chem bio weapons if a bomb is used at the marathon. The fedzilla had prior data on possible attack and were probably very concerned that the threats of radioactive material bombs would be used. Those big packs would have had chem bio hazard suits with breathing apparatus and detection equipment. At least one of the photographed guys has on a seal symbol hat.