He could have been driven to crackpottery also.
Consider this hypothetical: A person in intelligence knows something you would rather didn't get out, but you suspect there's a chance they will leak it. Maybe they have a personality that leads you to believe they can't in good conscience keep that secret, or maybe you're just callous and paranoid, doesn't really make a difference.
One thing you could do is convince them of something completely ridiculous that no one will take seriously. Even easier if there is a large existing community of nutters that already believe that (possibly you manufactured that too, just for such an occasion). Put on some little shows, make sure they see some documents they "weren't supposed to", and when they've bought into it enough have someone all but confirm it to them in person.
Then, if they're in a leaking mood, they'll discredit themselves for you.