Apparently, someone felt they needed gas for their vehicle more than I needed it for the lawnmower.

I really don't begrudge them the gas. I understand the desperation that drives some people. But they took the gas can except for the seal cap, meaning they won't be able to actually use the gas can to store gas.

And there is the issue of the additives that I put in the gas for the lawnmower. It will probably kill their catalytic converter.

Inconvenient for me. Ultimately more inconvenient for the thief.