Making it a crime gives the police the power to take measures to prevent it.
They were pointing the gun at each other and pulling the trigger.
Pretty sure suicide actually is a crime because if you damage some one else or their property in the act, even though you are no longer physically present to prosecute, those harmed or damaged by your action can seek redress in the courts. IOW if the rifle round you fire through your head goes on to kill a 7 year old in the next house your estate can and will be sued.
Court after court after court has ruled that the police have no duty to protect.
Ask any one of thousands of people who have been "protected" by the police when an ex-spouse, ex-lover or stalker has repeatedly violated a protection order.
You may need a ouija board...