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.<p><pre><code> ... 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.</code></pre>