It would be bizarre only if such security measures were perfect. They're not, so it's not bizarre, though anybody getting in is still unlikely, assuming they don't have weapons. Yet Lanza did have weapons, so again, it's not bizarre.
All reports indicate that he shot his way into the school. A
security memo sent out to parents at the beginning of the school year mentioned that they would be implementing a new security system. I don't know where you read that Sandy Hook had bullet-proof glass doors, but from the memo, it appears that visitors did need to ring a bell and be visually recognized. But note the end of the letter, which states:
We need your help and cooperation for our system to work effectively. Our office staff is handling multiple tasks. Though they will work diligently to help you into the building as quickly as possible, there may be a short delay until someone can view you on the handset and allow you to come in electronically. There are times during the day when office personnel are on the telephone, addressing student concerns, or in the copy room; there are other times when only one person is in the front office.
Aside from a sign at the entrance saying "Sandy Hook Elementary is a Gun-Free Zone," that's a pretty good scenario for a crazed shooter: a decent security system, but no one manning it.
The only mentions I see of no broken glass, bullet-proof glass, or no video footage of Lanza come from less than credible places. If I'm going to comment on that I'll need to corroborate it with better sources. I see where you're coming from, but as is constant with the nature of conspiracy theories, the connected dots are very flimsily held together.
The
video you posted below refers to a Fox News report. When was that report from? The day-of? The report before it was aired Dec. 15th, one day after the shooting, and they said Lanza's rifle was found in his car. It's indicative of more incomplete reporting.