Strafzaak means “criminal case.”
You may see the plural, strafzaken, in the archival descriptions of court records. The finding aids often have separate series for criminal records. These may include the case files or verdicts.
The severity of the crime determined where the case was tried. For each place where my ancestors lived, I try to find out which court had lower jurisdiction and which had higher jurisdiction. Major crimes, like murder, arson, or grand larceny, would be tried by courts with higher jurisdiction.