Killing the slowly is likely in reference to the fact that critters such as possums and raccoons can not be trapped and relocated. Almost every attempt to do so outside of a controlled relocation results in the slow death of the animal by starvation or predation. This is from a university study:
Relocating raccoons, opossums and squirrels results in a high mortality rate due to various factors. Studies show that a significant percentage of relocated mammals die within a short period, with some reports indicating mortality as high as 95%. This is primarily because these animals are adapted to a specific home range, and relocation disrupts their ability to find food, shelter, and navigate their environment.