The first priority in a preliminary homicide investigation is to:

The correct answer is that the first priority when it comes to a preliminary homicide investigation, one must ensure the safety of the environment (the scene itself), then one must attend to aid the victim with emergency aid and to check whether the victim is still alive or to conclude that death has occurred or happened.

The first priority in the preliminary homicide investigation is after the scene has ensured its safety, the priority is to be able to provide emergency aid to the victims if the person is still alive and if the victim is dead base on the investigation.