You were there were you? You knew the alternatives etc?
It's not rocket science. If it was a bigger animal the options would have been to hit it with a car and risk the lives of the officers or to close the road. As it was a smaller animal it was easier to kill it by running it over than to close the road.
There's always an option to close the road. Roads get closer all the time. Therefore the Police aren't correct when they say that was the only option.



