If the person is unable to fill out the form, another person may fill it out for him, indicate that he has done so, and the reason therefor. A party files and serves a written demand for a jury trial not later than twenty days after service of the last permissible pleading.Jurors hear either criminal or civil cases. In criminal cases, a district attorney acting on behalf of the citizens of Pennsylvania prosecutes a case. Fill out the jury duty questionnaire your county sends you. History of Jury Duty. Here are some commonly asked questions that may help you better understand the Jury System. We recommend clicking on the "Show all answers" link below. This book is written for jurors selected to serve in the trial court of the Federal Government, the United States District Court. The charge of a judge to a jury in a United States District Court frequently is much more than a statement of the rules of law.