So. Taking into consideration the first sentence of this article...
Just exactly HOW is this a murder investigation?
In AZ, it would be a murder investigation due to Felonious Murder - a criminal act resulting in a death will garner murder charges on conspirators/participants in the original criminal act.
It’s a murder investigation because one of the perps is alive. He can be charged with murder because he was a part of a felony in which someone died. His partner.
If the story checks out as reported, then there should be no charges. It’s probably what happened.
But what if it doesn’t check out? Suppose you were invited over to Sheila’s house and her Dad shot you dead as you were walking towards the house. Then he told everyone you were planning a home invasion. You’d want someone to investigate and not just take the story at face value, wouldn’t you?
They should ALWAYS investigate deaths that are from unnatural causes.
“Just exactly HOW is this a murder investigation?”
Article does not say but in most(?) states you can charge the person assisting in the crime if his buddy is killed by the person attempting to stop the crime.