You would probably have to indirectly kill them or ruin their lives, rather than actually murder them. Like make them all lose their jobs and be unable to get new ones. Not sure how you would go about doing that though.
Or you could pay people to kill them. It would cost a lot, and you'd have to get the people you pay to kill them all at the same time, because after a few have been killed, it will scare the rest/put them on high alert.