One question for the FBI: why so much investigation over a crime committed by someone who is dead?

Based on the nature of the crime, I'm guessing there weren't many accomplices. The one guy who helped him get the guns is probably where they need to be focusing their investigation and interrogation. If ISIS helped him, how? He took a gun to work and killed people. That's not an elaborate scheme.

It does not benefit the FBI to lose goodwill with the American people over this case.