Mark Partridge was a Chicago trademark attorney who testified as a defense witness about sitting next to O.J. Simpson on the flight back to Los Angeles after the murders. Called by Johnnie Cochran and examined across multiple rounds — including cross-examination by Marcia Clark — Partridge's testimony occupied a full day of trial and centered on Simpson's demeanor and behavior during the flight, offering the defense a firsthand account from an independent professional with no prior connection to the case.