Tell them, very anonymously. You don't want to risk them accusing you of anything. Or, just forget it about it completely, which is probably the safest option.

Tell them, very anonymously. You don't want to risk them accusing you of anything. Or, just forget it about it completely, which is probably the safest option. Do not do anything destructive. It would be highly illegal and you could very possibly end up losing years of your life in prison. It's not worth it.