>>It is technically trespass. Visitors were required to sign in.<<
Disagree.
Once the person was buzzed in it is quite clearly an invitation to enter. There is no way for a person to know additional requirements unless told.
I think this was a great idea.
Something similar happened many years ago to a mainframe computer operations manager (Might be just lore). A DP auditor (we used to have such things) known to the computer operator was given access to the machine room. The auditor chatted up the operator and “accidentally” left his briefcase in the machine room.
When it was discovered a bit later, it had a note inside it with the word “boom!” written on it.
Ops manager, operator AND auditor were all immediately fired.
If what you say is true, it might not be trespass. I didn’t catch that he was buzzed into the school. I thought he blew past the front desk and as a result, they went chasing after him, then he ducked into his kid’s classroom, where he had not been given permission to be.