When Phil Zimmerman made PGP available to the world, he gave everyone with a computer access to secure and private communication with anyone else with a computer. His goal in doing this was to give the public a way to communicate with the assurance that the contents of their messages were private, an assurance that had not been available since advancements in surveillance technology such as hidden microphones and wiretapping had been introduced. His goal was not to facilitate the dealings of criminals and terrorists, his interests were in the privacy of normal people who just wanted secure and private communication.
Of course, whether it was his intention or not, there's no denying that PGP was used by criminals and terrorists and whoever else had nefarious intentions that they wanted to hide from authorities. Just because facilitating these people wasn't Zimmerman's intention doesn't mean that it didn't happen, but it seems unfair to place the blame for these people's actions on him. Just as we can't blame the hardware store that sold the crowbar to the burglar who used it to break into someone's house, or the winter apparel store who sold him the gloves and ski mask he used to hide his identity, we can't blame the maker of a technology when that technology is used for harm. If the burglar from our metaphor also used a silenced pistol he bought from the black market in his heist, that's different. The black market arms dealer who sold him the weapon had no illusions as to its intended purpose. He knew it would be used for a crime, and sold it nonetheless. Therefore, that arms dealer deserves to be charged with aiding and abetting the crime. In this analogy, PGP more closely resembles the crowbar and gloves and ski mask than the gun. Zimmerman didn't put PGP onto the internet to aid criminals, he did it to protect people's privacy. The hardware store owner knows that crowbars can be used for breaking and entering, but that's not why she sells crowbars, and she shouldn't be charged with assisting the burglar. Zimmerman probably knew that PGP could be used by criminals, but that's not why he published it, and he shouldn't be charged with assisting those criminals.