Why was the mosque attacked?
I am going to guess to kill a bunch of cops while they were gathered at the mosque.
White suprema-cyst rhetoric seems likely. 🤔
Like csvset said, it would seem at first glance the target was all the cops who prayed there.
I was in Jordan a few years ago. We had to cross the border on foot into Israel to catch a plane. We happened to get to the border at their late afternoon (early evening?) prayer time. They literally shut the border - nobody in or out - while all the people who worked at the crossing - from security to the passport clerks and even our tour guides - went to the mosque to pray. So thinking of that experience, if you wanted to target a specific group of people for political (not for religious reasons per se) then that may be one way to do it. You know they tend to pray at the mosque where they work.
Not to say it couldn't be both. One sect crazy guy wants to bomb the law enforcement of another sect. That could be possible too.