I kill about one person every few weeks, by not donating more of my time to effective charity. But that makes for a boring market, so let's limit this to actions that most of society would agree constitute killing someone. This includes but is not limited to:
Comitting murder.
Hiring someone else to commit murder.
Legally killing someone in self-defense.
Being drafted as a soldier and killing someone in a war.
Carrying out an execution for a prison.
Having legal authority over and consenting to a family member in a coma being taken off life support.
Agreeing to save someone's life in some circumstance, then choosing not to do so.
Some things that do not count:
Having an abortion.
Shutting down an AI that some people believe is sentient.
Voting for a political policy or candidate that results in people dying.
Choosing not to attempt to save the life of someone I could save but had no social responsibility over.
I reserve the right to resolve this market to NO at the close date if I perceive there to be strong external incentives for me to not resolve it to YES, even if I have killed someone.