Discovering the Truth
Marty could not believe that neither Eric nor Giovanni had the idea to just get rid of the evidence. Maybe it was cockiness that they would never be found out, or they were just stupid as could be. Either way, Marty now had the evidence he was looking for which he could use to confront the boys. He knew he could not take it with him as it would then be obtained illegally, but because it was in the safe, he could easily leave it behind.