I think the three people that purchased guns, bought bullets, planned on robbing a store, drove to that store armed with guns, proceeded to rob the store and began shooting at someone who was a security guard there and whose job it was to protect the facility were the real "instigators" here. What is not currently known is whether the guard shot first. But I'm sure he didn't wake up that morning and decided he would force the criminals to rob his facility. That was probably their own idea, hard as it may be to believe. They have free will. Instead of going to Disneyland, going to the park to have a picnic, or just at home to watch TV, these three criminals chose to do something that could result in prison time, injury or even death of any or all of them. They knew that going in. They were free to chose not to do this, but they chose to do it anyway, so in that way, yes, unfortunately for them and their families and friends, I'm sorry to say, they "did have it coming".
The fact is, these three criminals shot numerous times at another human being, and could have killed or maimed at least one other person. That security guard was a human being, and he may have had a family, friends, and people who loved him and would have mourned his death if just one of those 40 bullets that were flying that day would have killed him instead of the perpetrator of the robbery. Why doesn't THAT part of the story bother you?
Yes, you are correct- the criminal that died was a human being. So are pedophiles, mass murderers, and serial rapists. Hitler was a human being. So was the Hillside Strangler, Charles Manson, Joseph Stalin, Mussolini, Pol Pot, and Idi Amin. So are many of the criminals who chose to destroy other innocent people's lives and now have to live with the consequences of their actions. What's your point?