The most accurate and reliable method for determining witness truthfulness, is corroboration. Truthfulness is more important than credibility, because a witness can be credible and lying through their teeth. If you only assess how credible the witness is, you may fall for the lies of a credible one.
To stay on topic, the corroborative evidence for mass graves at TII comes from;
- every single Jewish Sonderkommando and SS camp staff, who worked there.
- the 1944 aerial photo showing disturbed ground and rectangular outlines
- the 1945 Polish site survey that found large areas of disturbed ground containing cremated remains.
- the digging by grave robbers from 1945 onwards, that unearthed cremated remains.
- the 1966 site memorialisation work, that identified areas of human remains, to then cover them with concrete to prevent grave robbing.
- the 2011 geophysical survey, that identified specific areas of disturbed ground and found cremated remains on the surface.
- the circumstantial evidence of mass transports of people arriving at the camp, and very few leaving.