In August 1942, he was ordered to Lublin reservation, where he was in short time drafted into the SS with the rank of Scharführer (Sergeant), dispatched to Operation Reinhard, and sent to Treblinka extermination camp.
Matthes as remembered by Jerzy Rajgrodzki, a prisoner in the extermination area: He used to beat the prisoners with a completely expressionless, apathetic look on his face, as if the beatings were part of his daily routine.