If you listen carefully to the sound on the video, between when he starts shooting & enters the prayer hall, (about 15 seconds), there's the sound of a window smashing in the background. This was a father with his 7 year old son, who smashed his way out & appears now to have become the only 2 in the prayer hall to survive. The reflexes involved are phenomenal.
Sites hosting the video are under mass attack now with 5 eyes consensus the video be destroyed wherever it exists. Way too late. Within 2 hours of it happening it was being shared far & wide, publicly & privately.