Had the man’s injuries been caused only by being thrown through the
windshield, there would have been no blood on the front seat of the car.
Therefore, the Professor knew the blood on the seat had been caused by
injuries to the man, with probable murderous intent, before he was
thrown through the windshield.
His assailant had killed him, started the car, and had then hopped off
the running-board, hoping the wreckage would cover the murder.
Forethought we may have, undoubtedly, but not foresight.
Napoleon.