From what I have read, the elements of the conspiracy offence are a
plan to commit a crime involving multiple individuals, and at least one overt act taken in furtherance of the plan. For example, if people get together and plan a kidnapping, then one member goes out and buys some rope, that could be enough to represent conspiracy to commit kidnapping. You don't actually have to do the kidnapping to be convicted on conspiracy. If Bell got together with his friend and talked about disabling government computers with "carbon fibers" (whatever those are), and he then goes out and buys a source of carbon fibers, a case could be made that this would represent the crime of conspiracy. (We don't know yet whether either of these thing actually happened, of course.) Now his lawyer can argue that the conversation was purely hypothetical speculation of the type which technically minded people commonly engage in, and the carbon fiber source (if it exists) was acquired out of curiosity based on the discussion. Then it would be up to the jury to decide whether Bell's actions actually were part of a planned crime or not. In this context his writings and hostile relations with government agencies could conceivably be used against him, if his lawyer did try to argue that his conversations were just innocent speculation. Hal