Your husband needs to get a retained or court appointed attorney to challenge the basis of the detention.  If the detention was illegal... which is sounds like it was... then the case will be thrown out.  To prove that the officer had no basis for the detention and subsequent arrest, the attorney will need to get a copy of the patrol video or a copy of the body mic that the officer would have been wearing.  He doesn't need to pled guitly to something that he didn't do.