Alabama does indeed have lax gun laws, but I don't think those laws had anything to do with this. Owning a handgun is perfectly legal in every state. All Miller is known to have done is receive texts from Miles asking him to bring his (Miles) gun to him. Miles then provided that gun to the other guy, who committed the murder. Without being able to prove that Miller knew that the handgun would be used for a murder, there really isn't anything that would be a crime in Alabama or any other state unless Miller himself had a criminal history that prohibited his possessing a handgun, even briefly.

I do suppose that some states have different laws as to what age you have to be to even possess a handgun (as Miller did have sole possession of a handgun at least for the time it took to retrieve it and deliver it). In Alabama, the age is 19. He might have been legally too young to deliver the handgun in some other states, admittedly.