Details are emerging about the Orlando Pulse Massacre. It is clear that some of the first impressions were false.
First, there was not any initial exchange of fire inside of the club. Officers did not fire at the murderer in the club, or he at them, until the last few minutes, three hours later, when SWAT officers broke into the bathrooms through a wall.
There was an initial exchange of gunfire, but it was outside of the club. The off duty police officer/security officer quickly disengaged as the murderer entered the club while firing. It is precisely the scenario that John Lott has often predicted. If a security officer is known, a person planning a mass killing will determine a way to take them out with a surprise attack, find a way to bypass them, or avoid them.
Second, there was some time from the initial shooting until police mounted an armed response. The police response was very quick. Additional officers arrived at the scene, formed up, broke out a large window, and went in. But it still took time. It appears about six minutes passed from the initial shots until the police entered the Pulse club. During that period, the murderer was shooting and killing people inside the club. The shooting continued as the police entered.