Final answer:
William Denson would use direct testimonies from liberating soldiers and physical evidence such as U.S. Army aerial photos and witness accounts from trials to prove the harsh treatment of prisoners at Dachau.
Step-by-step explanation:
When US army prosecutor William Denson began the Dachau trials, he could use several facts to his advantage, but one of the most compelling pieces of evidence likely to be used was the direct testimony and the physical evidence found at the camp upon liberation. This includes the U.S. Army aerial photos such as the one showing the concentration camp at Dachau, which provides a layout of the camp, supporting the scale of operations with barracks, hospital, and storehouses for the guards. Additionally, eyewitness accounts from liberating soldiers, like the remarks from Felix L. Sparks at the U.S. Holocaust Museum, reveal a firsthand encounter with the aftermath, including sights of emaciated corpses and the overwhelming stench of death, contradicting any arguments made by the defendants about prisoners not being treated harshly.
These firsthand narrative and visual confirmations, complemented by evidence presented at trials by liberators, such as photos and senators witnessing atrocities, and the liberation of other concentration camps like Auschwitz, Buchenwald, Bergen-Belsen, as well as the orders and tactics disclosed by SS officers in trials, unequivocally expose the systemic brutality and mass executions orchestrated by the camp officials.