The FBI seems to have gone further than usual (in my limited understanding of what is usual) here with "assisting" the man to incriminate himself. To me (not a lawyer) it sounds a little like entrapment.

  ... an undercover FBI agent posed as a person who could assist him.
  According to the complaint, Varnell took a series of actions to
  advance his plot. He identified BancFirst as the target, prepared a
  statement to be posted on social media after the explosion, helped
  assemble the device, helped load it into what he believed was a
  stolen van, drove the van by himself from El Reno to BancFirst in
  downtown Oklahoma City, and dialed a number on a cellular telephone
  that he believed would trigger the explosion.
  
  Varnell is charged with attempting to use explosives to destroy a
  building in interstate commerce.