I am a veterinarian, and when I was a resident, I made sure that my neighbor's very sick cat (who I knew they wanted to euthanize) died before they got home from work.

I was a veterinarian at a private (not a shelter) animal hospital. Sometimes owners would bring in very old, very sick animals, and mention to the vet and vet techs that they wanted to euthanize them if it wasn't possible to cure whatever the problem was. Once the test results came back, the vet would call them and they would come in and do it officially. Well, my neighbor had a very old cat that was allergic to some cat food, and she kept feeding it that food. The cat was always sick, the cat had a lot of dandruff, the cat had scratched its ears until they were bleeding. They brought the cat to the animal hospital, I asked one of my colleagues to run extra tests, but then when they got the test results back, I told them to wait to call the owners until after 6pm. In the meantime, I found out from the test results that the cat had a large mass in its lungs and had severe kidney disease. At 5:30, I told my coworker to give the cat a lethal dose of potassium chloride. I then removed the cat from the computer system, and went home. At 3am I received a call from the vet telling me that they had gotten a call from the owners, and the owners were very confused because when they came in, there was no sign of their cat. The vet (who worked the late shift) told them that they must have called the wrong animal hospital. It was a weird night, the owners kept calling, and they also kept getting calls from an unknown number. One of the vet techs answered the unknown number, and it was me, telling her that I had taken the cat to be cremated, and that it was very kind of me to do this because the owners live far away. the vet tech believed me, and was able to calm down the owners by telling them what I had said. It's been two years since that happened. The owners eventually replaced their cat, and when they see me outside, they always smile and wave.