The value of life is relative
There are people I would die to save, and there are others I leave hanging by their fingers from the edge of a cliff (yes, I'm petty).
The concept of placing value on non-human life seems to have come about from the fact that we as a species are no longer spending every waking minute fighting for survival. It used to be that creatures fit into two categories: prey and predator.
Then we learned a bit about farming and we got a third type of animal, the tool.
And we still continue to evolve in how we deal with animals. Although often too slowly to save many species.
As for the threat of the Gorilla, he posed a threat of injury but the chances of him actually killing someone were pretty remote. They'll knock you stupid but they're not mindless killing machines. The cops don't know that though. They have to protect the public, and also avoid getting sued because just by letting it live one minute longer and smacking someone around they put the city at an even greater risk of liability.
When it comes to city budgets the life of a single gorilla, or a taxpayer for that matter, means little or nothing.