I am inclined to go ballistic at the school. Clearly he is partly to blame and should never have left the school premises but surely they are required to prevent this!! He left something in DH's car and left school to see whether DH was still around (it was first thing). School is in the middle of a red light district (nice!) with lots of dodgy types around. Also on a very busy main road with trams going down a hill and a blind corner.
How "understanding" would you be with the Head (who is due to call me back). There is a security guard on the gate who presumably either saw him and did nothing or wasn't paying any attention.