I found this. It has more details, but still is just odd.
I would say they were there doing this:
“Over the years, the unit, which has a little fewer than 100 agents, has responded to roughly 850 episodes, including the bombings at the Boston Marathon last month. In that instance, agents from the unit were sent from Quantico after the attacks to deal with finding other explosives in the city. They have also responded to episodes in Iraq and Afghanistan.”
From that article, it seems they were no where around Dzhokhar. I’ll set the tin foil aside on this one.