"Accomplice" isn't even a legal term in the Alabama criminal code. It's just "accessory" or "complicity". The Alabama law that is colloquially called the "accomplice law" sometimes can result in Death Penalty charges for doing even less than Miller did.
Section 13A-2-23
Criminal liability based upon behavior of another - Complicity.
A person is legally accountable for the behavior of another constituting a criminal offense if, with the intent to promote or assist the commission of the offense:
(1) He procures, induces or causes such other person to commit the offense; or
(2) He aids or abets such other person in committing the offense; or
(3) Having a legal duty to prevent the commission of the offense, he fails to make an effort he is legally required to make.
(Acts 1977, No. 607, p. 812, §415.)
Ala. Code § 13A-2-23 - Criminal liability based upon behavior of another - Complicity. from 2018 Code of Alabama
law.justia.com
Like I said, he's only saved by the plausible deniability that Miles was going to do anything illegal. But any reasonable person knows that someone begging you for a gun at 1am in the morning isn't going to have many legal uses for it. Even if he was "only" brandishing, even if he was "only" going to threaten someone, those are both illegal so it's still criminal liability based on Section 13A-2-23 and that in turn would make him liable for everything that played out from there.