AMSTERDAM — In the aftermath of World War II, more than 300,000 Dutch people were investigated as collaborators, from men who volunteered for the German army to those accused of betraying resisters and Jews, who were often arrested or sent to their deaths. More than 65,000 accused collaborators ended up standing trial in a special court system that stripped some of certain civil rights, sent some to prison and condemned others to death. Most of the cases were resolved by 1950 and the filings of the special court — including police reports, witness depositions, material evidence and photos — were...