Dear District Attorney

I am going through the Citizenship process and have passed all the steps except during my interview it came up in the system that I had been arrested six years ago. I remember being taken in voluntarily for questioning on drug related matters pertaining to my brother inlaws. I wasn't even Mirandaed they asked all sorts of questions and no charges were ever pressed but the officer in charge of my citizenship case asked that I get a letter from my district attorney saying that all charges had been dropped. Please can you help me with advice on how to get my point across in a timely matter.