Very sorry to see this, I hope the vandal experiences a painful death. For what it's worth, those parallel marks look like they were left by a fork, rather than a key. Of little value I'm sure but perhaps that might help with your investigation.
2011.5 LeMans Blue e92 DCT, ZCP, European Delivery. Edition Grilles, Reflector delete, Rear Fogs Enabled, Borla/Encore Innovation Exhaust, LUX Angel Eyes, 255x285's, Dinan 3.45 Rear, BPM Stage II. "Last of the V-8 Interceptors, a real piece of history..."