He may have had an accomplice
An accomplice, perhaps.
Your statement, in trying to picture how this happened, leaves a number of questions.
“Police (an off duty cop doing club security, and 2 others nearby) engaged him in a gun battle even before he got inside, at the front door, but he shot his way in and they didn’t follow him in.”
I’m sure that’s how it’s reported, but it would indicate either that he was being trailed or was assisted.