First step:

Examine the person who may be dead.

Their pupils should be fixed and dilated–that is, showing no responsiveness to light and remaining fully open. They should not have a blink reflex when something brushes against the cornea of the eye. They should have no heart sounds for one minute of listening. They should have no breath sounds, and no other evidence of breathing. They should be unresponsive to deep painful stimuli (e.g., pushing down sharply and rubbing the sternum–the middle of the chest). Especially if they have been brought from somewhere else rather than dying in the hospital, they are “not dead until they are warm and dead”, because hypothermia can mimic death by slowing down and dampening down all bodily functions.