Who is liable for damages in this situation?

Note: This situation has no basis in a real-life event. It is the basis for a novel that I am writing. I do not need any detailed legal advice, just an overview of "who" is legally liable for damages in an event like this if it were to happen in real life.

A person is shopping at a convenience store when two masked gunmen rush into the store to rob it. The store owner immediately pulls a gun out from under the counter and opens fire on the robbers. One robber is killed immediately, the other continues to exchange gunfire with the store owner, is injured but survives. One of the store owner's bullets misses and robber and hits the innocent bystander in the spine, leaving him with partial paraplegia and PTSD.

Who is liable for damages to this customer? In other words, who would be ordered by the court to pay out a large sum of money to this person? The store owner, personally? The insurance company that insures the store against injuries that might occur on the premises? The surviving armed robber? All of the above?

Thanks in advance! :-)