The hard part isn't anonymously leaking the information. (You could do this with a $0.15 envelope and a stamp. Just remember not to put in your address as the return address and to wear gloves).

The hard part when you leak is that you are now in a set of people that knew the information. That usually boils things down to a handful or even one suspect. With US federal agents where in fact it is illegal to lie to them, they will have you in their office by lunch.