Misuse of the language - no hostages- people sheltering in place- if PP was target, why no attacks on those inside- reports from initial witnesses tell a different story- whole thing is strange- why is this taking so long?
Better safe than sorry.
Because it is extremely difficult to clear a building when there are non-combatants inside and you don't want to kill any of them in a cross-fire.
Also, the shooter is armed with at least an automatic rifle (AK-47), bullet-resistant armor, and lots of ammunition. There may be other nasty things as well in the two duffel bags that he carried into the building.
The Police would like to go home tonight.