It has been mentioned, long ago in the threads Kagey, but not too much was made of it. One would hope that LE was all over that.
There was construction going on all over the school. We went to my daughters preschool graduation and they had the gym divided with a huge piece of plastic. On the other side they were rebuilding or adding on. I know that they were there working before that too because there was a report of a guy falling off some scaffolding, or it fell, something like that.
Even though it's a holiday weekend, I would be surprised if they weren't out there tomorrow trying to finish up before kids head back to school on Tuesday.
I have been by there several times after hours and never seen anyone watching the site. It doesn't mean there wasn't someone there because some of the work they did would have had to expose areas where entry could be gained.
I counted about 10 guys, but as you know, when contractors with specialties come in, there can be many different groups. Electricians, plumbers, HVAC guys and the actual construction guys. This would have provided an opportunity for many people to come through. However, I think it unlikely since it was 9:15pm on a Friday night. Seems like everyone would be gone from the work site by then, looking forward to the weekend. Just my take on it though.
As for your other questions, I don't know the answers to those. Sorry.
What I can see construction might have started around May 7 2009.
http://web.me.com/anthaholt/School_Construction/May_7_to_21.html