It increasingly sounds like the armed guard at the school was following orders and didn't go into the school because it was radioed to him as firecrackers on the sports field. Who knows exactly what happened but I'm not comfortable with all of this talk of cowardice.
From a guy who we know would gladly use a baby as a human shield:
https://www.theguardian.com/us-news/2018/feb/26/gun-control-laws-nra-congress-return-recess