8 Year old locked in a School

Who in their right mind would lock a child in a big school alone so that you can ****** off home??? I mean really? How did you sleep last night? So my sons transport doesnt pitch and the school phones me to pick him up and at this point im in a tis trying to get there as soon as possible but due to traffic and such i get to his school a little after 5 pm (and yes i know its late but it was an unforeseen circumstance) to find him locked inside without a soul insight!! How do i explain to my son that he shouldnt be afraid of school because thats not whats suppose to happen?! No excuses being made but seriously? Would it have been such an inconvenience to wait till my son is safe with me? I'm actually quite ****ed off that a school would do something like this! The very place children should feel safe at became a fearful place.