I've heard said that rather than Bremer dismantling any authority including police and army, it was a situation of these personnel abandoning their posts. It's true that Bremer could have taken a course of action making public announcements encouraging their return. But it wasn't the case of Iraqi being on the job and Bremer dismissing them.
But there were probably errors in the planning in this regard- getting rid of Saddam regime was probably stressed too much, and emphasis on maintaining the existing order was not. Though, de-Bathification in general was reasonable, probably too much emphasis was placed on it particularly earlier on, and perhaps had there been propanganda which had announced before Iraqi had left their posts that there would be an effort to preserve the existing order, but those not loyal to new regime would be removed, things might turned out differently.

So, even though what is said in this article is probably mostly correct:
http://hnn.us/articles/4624.html
I think there is more to this story.