Is the driver liable for blood money and expiation, given that he ran over a man lying on the road, and it was found that the man had been stabbed before being run over, and the driver does not know whether the impact or the stabbings caused death?

If the driver was moving within the permitted speed limit and did everything possible to avoid the collision but was unable to, then there is no sin upon him, nor is he obligated to pay blood money (diyyah) or expiation (kaffarah), whether the man died from the impact or from being stabbed. The driver is absolved of responsibility if the accident was the result of an irresistible force (force majeure) that he could not repel, or due to the act of the injured party himself.