He doesn't need to have it proven that he hung up with the intention of having the victim die. Once again, this is not the issue. He had the intent to hang up and leave them by themselves with no guidance or instructions at all. Look at how much public backlash and outcry there is. This is a serious motherfucking issue that this guy just hung up on people who needed his help.
He was a man in a position specifically designed and instated to help people with situations like this and was meant to uphold an image and reputation that people in situations such as the one the callers were in can innately trust to give them proper aid.
If the way he hung up on them wasn't 'intent to leave them alone and without the guidance of what was supposed to be a trusted and professional operative' in your eyes, then I don't know what other words to tell you.