I'm more concerned that evidence is deleted by some automatic process on their part. What happens if the guy appeals? If the working storage is really limited for some reason (and it had better be a good reason in this age of $100 3TB HDDs), then archive the data off before you delete it.
Maybe this was the whole MegaUpload filestore and it was really straining the servers? Even then, the deletion should have been a manual act done by someone who can be held accountable for not checking the status of the case before pressing the delete key.