If he does not have one already, you need to hire an attorney for him immediately. Preferrably one with trial experience. Usually there are more facts and more to the story than what is presented here. An attorney can help sort things out.
Your husband is facing the same time in prison that the robber himself is, as a conspirator or principle - 30 years. If your husband did not know what was going down, he may be innocent, but he has to convince a jury of that.
It sounds like he has a good defense to the charge. However, he needs to get a good trial attorney to fight this. They can cross examine and depose witnesses and hopefully show the weaknesses in the state's case.