Terrific. Then what? It's not like Assange is carrying 300K documents on his person. Those are electronic files shared across a distributed network. There's no way to stop their dissemination. Once the documents were stolen off a "secure" server, they were as good as published.
The question isn't about how do you stop Assange, the question is how do you let a 20-year old E-3 have unfettered access to such material. That's what needs to be investigated.
No, it wouldn’t stop what has already been leaked, but
IT SURE WOULD SEND A MESSAGE !!