In the case of the San Ramon pawn shop robbery, the actual theft had not yet occurred when the robber was shot by the store owner. The four boys walked into the store with tire irons to smash and grab, but the grab had not happened yet when he was shot.
How can one label it a "felony" murder when the theft had not yet taken place? Does the robber have to have the property in hand in order for it to be valued to see if it meets the felony threshold? Does it matter if he had grabbed a $100 watch vs. a $1,000 necklace?
-PJ
The general rule is that if a homicide takes place during the commission of a felony, the participants in that felony are responsible for the homicide as felony murder, usually a lesser form of murder, with lower prison terms. Often, the question becomes whether they were still in the process of committing the felony. In the situation you postulate, the question is whether the felony had started already. There are 50 states each with their own history of determining the answers to these questions, so the case law is all over the place. You'd have to look at the state law first.
To answer your question of how it can be labeled a felony before the theft, you have to know what felony the prosecutors charged under, then look at any case law that says when that felony has occurred. If the felony was "entering a store with intent to rob", or "conspiracy" or something like that, it may have begun the minute they entered the store, or before they entered.