As someone else noted in another thread, Hersh's reputation and the source are absolutely evidence. What he hasn't provided is hard proof for the claims.
I can't find any proof whatsoever as to who actually did it from the western authorities claiming to investigate it either though. In fact, there's been little to no news or updates at all since the incident.
The code name was "Gouda", it was established that it was the Swiss Vatican guard. Ementaler would have been too much into the face and the Vatican wanted to avoid problems with the Italians, so Parmesan was of the table.