how do I know someone hasn’t placed a bomb inside
You learn enough about electronics to identify things that shouldn’t be in there, and then you open up and analyze your devices.
Alternatively, you could not become involved with an organization that is at war with a powerful country who has a capable spy/espionage agency.
You assume the FBI, secret service, and every other 3 letter agency who can get access to his cell aren’t doing exactly that?
Given his biography, I would expect a string of conspiracy laden answers and generally incoherent explanations, though.