On: How to Leak to the Press

[adlpz]

That should do it too, you can even make it yourself with a piece of cardboard and a sharp knife.

[monsterix → adlpz]

Probably take fingerprints of someone on the envelope too? Randomize it and complicate it so much that the idea of finding you dies the most desperate death.

Ha ha, the situation feels 'arrived' at fictional level already!