I disagree with not issuing the alert. They knew before midnight that they had a REALLY big problem. Multiple victims and fires blazing. It didn’t matter if they knew who it was, they just needed to send an alert so people would know there was a madman with a gun that was burning down houses.I don't think they had sufficient information to issue the alert until the morning after, once they'd spoken with the GF. Before that conversation, did they even know who the perpetrator was? And even if they'd known who they were looking for, they every reason to believe he was contained within the two perimeters they'd set up around the area - they hadn't caught him and as far as they were aware, no civilians had been allowed to leave. Obviously we know now that he'd escaped in his homemade cruiser, but at the time, that would have been inconceivable to the officers at the scene.
With this in mind, it's understandable why the alert would have been viewed as unnecessary at that point. This is purely speculation on my part, but with no other apparent reason for the gunshots to have halted, maybe they thought the perp had died in one of the structure fires? Maybe they thought the perp was one of the "several" victims in the area? They would have needed more time to investigate all the different crime scenes, but they had no reason to believe he was outside their grasp.
However, with all that said, once the info from the GF came that morning, everything changed. I personally feel it was very ill-advised and irresponsible to rely on Twitter alone rather than issue an emergency alert. The alert would absolutely have reached more people more quickly, and almost certainly would have saved several lives. I hope that many people around the world have learned from this horrible situation.