In the comments after Bruce's article, Galen Cook says that there are witnesses to the jump, presumably from the ground. The plane was at 10,000' MSL. A quick Google search puts Vancouver's elevation at a couple hundred feet. On a clear day in broad daylight, it would take a familiar eye closely watching to see someone exit the plane. On a clear night, no you couldn't see the exit, you'd be hard pressed to notice the plane. On a cloudy night, not happening.
Unless they saw him landing, in which case the FBI would know exactly where to look.