Sad story, over a dog. Good first thought; don't kill, or be killed over a dog, or cat, or goat, or... OK, so now; just my $.02, THE COP WAS THE BAD GUY. There are good cops, and POWER TRIP cops. He tried to bully the old dude, got called on it, and shot him when the old dude stood up for his right to be armed on his own property. THIS SHOULD NOT HAVE HAPPENED!!! Even if the old guy was crotchety (like most of us old guys - see Clint Eastwood in Gran Torino), the cop should have talked to him calmly, and CALLED IN A SUPERVISOR to work through the situation, if he "feared for his life". If the homeowner declined to surrender his weapon on his own property, which, by the way, IS HIS CONSTITUTIONAL RIGHT, the cop should have backed off, de-escalated the situation, and called for help to resolve the situation peacefully. Instead, it sure looks like he got mad that the old guy didn't bow down to him, and tried to disarm him with force (likely after some choice words and big threats). Even if the old guy was plain old NUTS, he has the right to carry on his property, if this is, in fact, what went down.
If this is what went down, did the old guy also display poor judgement? YUP! You discharge a firearm, and call the police about it, you likely should not meet them in your front yard with a weapon... That said, we, as CHL holders are trained to defuse tense situations so that deadly force is not required; it's clear this officer either did not receive this training, or determined that it did not apply to him.
