How is it that my attorney believes he can get my DUI dismissed from court?

I had gotten a dui in february and blew a 2.0 and while I was in jail I asked around about the best attorney in town so they told me the name of a guy.... he was not cheap to hire but sounded like my best bet. He said that we would take it to trial and basically try to get the paper that said how high I blew dropped as evidence do to the the laziness of the cop that did the arrest. long story short I was wondering how it is during trial the operation this guy is going to be able to convince a jury.when at the beginning of the trial obviously im guilty as sin but after, he if he can get this evidence dropped the jury could find me innocent or can the judge step in and drop all charges cause the state has no evidence then the jury can't deliberate? I don't know exactly what all it is that im asking but how would a case like this be preceded in the judicialsystemm?