Found something a little weird in an article about the Florida shooting.

This could very well be nothing, but I found a line that stood out to me a little.

Police officers arriving on the scene from the adjacent city of Coral Springs thought the gunman was still inside as they searched the building, based on a security camera video feed that they mistakenly believed was showing them real-time images but was actually footage from 20 minutes earlier.

My question is this: why would the security cameras in the school be delayed by 20 minutes? That seems like it would do no good, and even cause several disruptions throughout the day, not being able to see live video.
I could just be missing something. Maybe they rewound the tape to see it before the police got there (but what good would that do? Why wouldn’t they tell the police that they had done this? Wouldn’t they be able to tell by listening for gunshots and coordinating with other officers?).
Too many things in this story are too coincidental for it to just be “another fucked up kid with a gun”.
Remember: the guns aren’t the issue.
Link: https://www.yahoo.com/news/armed-deputy-florida-high-school-resigns-failing-engage-001502726.html
 
h/t AC