Traces of the attack

Exploration Stage: Scientist's Mansion
From: Albert Wise
Description: After the break-in at Charles' house, the killer probably tried to cover his tracks, but he was in such a hurry that he couldn't cover them all! Look at the door sill. See the drafting compass stuck in there? Pull it out!
Completed: Thanks for pulling out the drafting compass. I couldn't have reached it myself. But why was it stuck in there anyway? Charles is a clean freak. Did he use it to try to fight someone off?