Hello Mr. Wetmore,
Have you tried submitting your request through the Contact Us page on nara.gov? Contact the National Archives | National Archives
It will take a few weeks to get a reply but the response will be from a reference archivist familiar with the DoJ records. If the information you need can be found within a few hours or less and we don't need further clarity, we can send you our finding and you'll arrive with the box information beforehand.
The prosecution files are usually part of the court records in record group (RG) 21. Since this case took place in Washington, DC, the records should be at the Archives building in Washington. You can email Archives1reference@nara.gov to inquire about these records. Usually, they're arranged by the docket number assigned to them by the court, but if you know the name or names (e.g. Smith v United States) and the year, the staff there should be able to find it and get you the information you will need to access it.
There may be additional files in RG 60, General Records of the Department of Justice (DoJ). RG 60 materials are located at The National Archives at College Park, Maryland | National Archives. There is a general index for these files (https://catalog.archives.gov/id/1882794) covering the years 1904 to 1951. It is searchable by name. There is no online or electronic resource for this index. You or someone you designate will have to come out to College Park and go through the index in-person. Alternatively, you could email your list of names to them at Archives2reference@nara.gov but they can only do ten names per request. Once you have the classification number, you will then need to request those boxes in turn. Given the number of defendants, this could take more than one day to complete.