Reference

Willem van Eijk, known as "Het Beest van Harkstede," was a Dutch serial killer convicted of murdering five women between 1971 and 2001. However, he was also suspected in several other unsolved cases. Specifically, he was considered a suspect in three additional murders:

1. Cora Mantel
2. Aaltje van der Plaat
3. Sasja Schenker

These cases remain unsolved, and while Van Eijk was linked to them, there was not enough evidence to charge him or prove his involvement definitively. His criminal activities have garnered significant media attention and are often discussed in the context of cold cases and serial killers in the Netherlands.

You can find more detailed information about Willem van Eijk and his crimes on Wikipedia and Murderpedia here.