We can send the Tower an anonymous letter with just "destruction of X location is the result of a Leaf research experiment that went awry, not hostile action, don't panic" and some Leaf security codes for identity proof in it. Now, sure, the circle of people who could be responsible would be easy to infer and pretty small, but the letter wouldn't really provide any new information to him: if Asuma doesn't assume it's hostile action (which we very much want), he'd have to assume it was done by Leaf, and then narrow the culprits down to the same people. By the letter, we just (1) cut off the possibility that he calls up a Clan Council in a panic (in which case we may be forced to reveal our responsibility, or at least leak way more information), (2) make it clear the scale of destruction was unpredicted, so he doesn't need to chew anyone out for that either.