you have absolutely no idea what data they have or don't have
Well, that's not really true:
The FBI has confirmed that Russia alerted the agency in 2011 that Tsarnaev had ties to 'radical Islam' groups in his homeland. Homeland Security sources have also revealed the agency received tips in 2012 about his ties to extremists connected to a Boston mosque. (...) Tamerlan was said to have been named as one of the radicals that came to attention of an informant working with an agency attached to the Boston-area Joint Terrorism Task Force
Well, that's not really true:
The FBI has confirmed that Russia alerted the agency in 2011 that Tsarnaev had ties to 'radical Islam' groups in his homeland. Homeland Security sources have also revealed the agency received tips in 2012 about his ties to extremists connected to a Boston mosque. (...) Tamerlan was said to have been named as one of the radicals that came to attention of an informant working with an agency attached to the Boston-area Joint Terrorism Task Force