I am sorry this happened to you. As I read your post, I was mad and thought there is no way I would've let it go that far.
If that happened to me, I would've told the employees to immediately let me out a back door or one of the locked doors, but if they continued to keep me locked in, I would press charges for kidnapping and sue them and the company. I don't know how they think they can pull off that unlawful behavior.
I don't know nor care about what can be done about the beer theives, but the employees can't keep you locked in against your will. Yes, the beer theives were wrong for stealing, but don't lump me in with them.
If I were you, I would talk to an attorney and see if there is something there.