In a 2016 documentary about an art forgery scandal involving work by Heyboer that was first reported in 2012, the former Amsterdam "Anton Heyboer Gallery" owners George Knubben and Couzijn Simon were portrayed as having purchased "Haarlem-period" Heyboer works starting in April 2004 possibly coming from a collection formed by Santen.
[2] Experts claimed that if genuine, the works may have come from an "old Haarlem collection of etchings".
[2] One of the etchings shown in the documentary is signed on the back along with names "Josef Santen" and "Frans Verpoorten" written in such a way that the name of town "Santpoort" can be read.
Both men were colleagues of Heyboer before he spent some time in a psychiatric institution in Santpoort.
The collection is still untraced, but were returned to Knubben and Simon, who still firmly believe they are genuine.