Well, data that the Police is keen to share with as much of the public as possible, as quickly as possible. It hardly seems out of the realm of the reasonable to use Amazon for something like that.

They also want to use Alexa for incoming crime reports and internal discussions.

Things that get published in news media all ready, wanted and missing reports, crime info, etc..

Doesn't the USG put lots of citizen data on the AMZ gov cloud? Is that alarming in some way?

It all depends on the details. For pure storage of encrypted data it's probably OK. But I guess for an Alexa app the data will go through Amazon's algorithms and it won't be clear what else they will do with the data.

No Alexa skill owners usually have there own backend