imagine you are a detective examining a crime scene. you are trying to identify the person who commited the crime, so you collect samples at the crime scene. which sample would be most useful in identifying the person who committed the crime

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.