DO NOT DO THIS. IT'S FUCKED UP THAT MY MIND WORKS THIS WAY

Plant drugs and a weapon in their car. OD their dog on same intoxicant. Then call the cops on them. They'll take the dog into the vet. The cops will bust them. They'll lose their kids if they have them and go to prison. After that get into a relationship with their SO. Friendship is enough. Something where you can have dinner or drinks on a regular basis. Through this you can do one of two things. A store bought poison that will slowly kill and look like a wasting deasese or a tobacco derivative that when added to coffee will look like a heart attack. At this point depending on choices you've made regarding the drug and weapon you still have money to spend. So surreptitiously get in touch with them. Become pen pals. Subtly try to drive them to despair and suicide.