Simplify the following text for a Grade 12 native English-speaking person.
Original: Holocaust survivor Thomas Blatt , who investigated the subject , found little concrete documentation and no evidence of mass production of soap from human fat , but concluded that there was evidence of experimental soap making .
Simplified: Holocaust survivor Thomas Blatt , who did research of the subject , found little evidence of mass production of soap from human fat , but said that there was evidence of experimental soap making .