Prehistoric chimpanzee species used tools similar to those used by prehistoric humans; prehistoric tools recently found in East Africa are of a type used by both species  The area where the tools were found, however, is a savanna, and whereas there were prehistoric humans who lived in savanna habitats, prehistoric chimpanzees lived only in forests
Ttherefore, the tools must have been used by humans rather than by chimpanzees
The area where the tools were found was not a forest at the time the tools were in use.