I say a military chemical test gone awry, personally. They do random little tests all over the country. Seems like they could have done one in Desmond Cove that backfired, and everyone that wasn’t afflicted was evacuated. They probably set the mine on fire as an excuse, and as a way to prevent any further exposure. The deer probably wandered into town and either breathed in the chemical, drank contaminated water, or ate contaminated plants.

I’m really sorry about Teddy. I hope you can find some closure. Maybe reach out to a PI and see if they can dig anything up about the incident, and talk to the people that live on the outskirts to see if they saw anything strange. Of course, if it is military, I suspect they covered everything up pretty well. I wish you luck on your endeavor, and hope you share it with us when you go back!

(Seriously though, this story is good enough that I would read a novel based on it. Phenomenal job, OP)