"We want to look at everything that led up to an aggressive dog attack,"
"An aggressive dog can lead to an entire block losing mail service until the animal is brought under control."
That all looks after the fact to me. Was, brought, led, look at the tense of these words. Also note the word "normally"
Now if the breed or type of dog is banned altogether, it doesn't exist to cause the incident. That's proactive.
Let's see what's going on in Calgary "After years with Labrador retrievers at the top of Calgary's most-likely to bite list, pitbull and pitbull-type terriers have suddenly taken a dubious lead, passing both shepherds and retrievers."
In Calgary? No!
Article Biting criticism of dog owners | Columnists | Opinion | Calgary Sun Lets see what else we can find in Calgary about Pitbulls.
What does an actual Calgary resident think?Calgary Pit Bull Attacks
Lastly this link Pitbull Attacks, Maulings, and Killings