According to a recent article by Dutch public broadcaster NOS, two mayors have reported suspicions of election fraud because of the high percentage of votes by proxy in certain polling stations. The article states that this report is a standard procedure prescribed by the Kiesraad (the national electoral committee).
According to an article by Omroep Brabant the parquet has until next week to investigate these reports.
I wonder what the investigative process looks like. For example, is it normal procedure to ask (some of) those who voted by proxy whether they did so by their own choice?