Locked schools

In reading about the school shooter in St Louis the police said the building was locked so they did not know how the shooter got in. Before I worked as a sub teacher I used to go around and check steam boilers and recommend the chemicals needed for treatment. I went to many schools and often times would arrive in the early morning when the building was locked but I always knew there was a back door open for deliveries. Later while subbing in 14 different high schools it was common practice to have open doors until about an hour before school started. It would be easy for anyone to enter the building and wait in the restroom until after school started. That is still the case today. Most schools are very secure between 7 AM and 5 PM but other hours someone can get in undetected. It is the old saying that locks are to keep honest people out.