Even if that is so...which I doubt...why aren't they charged with the attempted robbery which resulted in a death?
The premise of Texas law is that individuals who are in the commission of a crime give up certain rights, including the right not to be shot and the right to blame the guy that's with you if someone dies while you're committing a felony.
I wondered about that too. One possibility that's still consistent with the details reported in the article is that the killer and his friends might have just been bumming around, when to the surprise of the friends, the killer said something like, "hey, come and watch this", and then pulled out the gun and began the robbery. They could have been too stunned or scared to either leave or try to subdue their friend, and then it was quickly over.
In a case like that, I probably wouldn't consider the friends criminally at fault.
Not to say that's what happened, just saying that there are scenarios where the friends wouldn't have actually been co-conspirators in armed robbery or murder.
On the other hand, if they *were* willing participants in an armed robbery, hang them high, even if they were surprised by the shooting itself.