I've been saying this multiple times, but reporting this is only keeping the ball rolling. All the anonymous assholes want is attention and perceived power. Report about it and you give them both. Don't report about it and you take it away from them.
This guy wasn't going to do anything. Who tells people they're going to bomb a school before they do it? This guy realized that a guy on twitter could make someone leave their house and then he realized he could change real life just by issuing a threatening letter, so he did.
This is not someone who is trolling people on a message board. Ignoring the threats does not mean this person will get bored and go do something else. These are real threats on someones life, and should be treated like real threats.
If these threats had been about an issue other than feminism would you take them more seriously? If it had been a result of: race, gun control, immigrant rights, or worker rights, would you be more inclined to believe that this person would turn to violence? Attacks like these are not unprecedented, so I'm not sure why you seem to think that anyone would be incapable of carrying out an attack like the one described.