The testimony casts doubt on a key prosecution argument.
Prosecutors say Amanda Knox and co-defendant Raffaele Sollecito killed Knox's roommate, Meredith Kercher, and then broke one of the apartment's windows from the inside to stage a burglary.
A stone was found in one of the bedrooms, with shattered glass on the floor.
The ANSA news agency said Francesco Pasquali testified Friday in Perugia, central Italy that the window was broken from the outside.
ANSA said Pasquali used a video to reconstruct how the stone was thrown.
Knox and Sollecito deny wrongdoing.