Well then he should be fine... I would go and see if there are RTA monitoring camera and what you can do about seeing the footage.
Wouldn't hurt to go and speak to the local police station and find out what they recommend. Has your mate reported the accident as yet? I have never had an accident which is my fault but you used to have to report it within a certain time frame. This may only have been for insurance purposes though?
If he reports it, with conflicting accounts of what has happened then the insurance company is going to have to investigate one would assume. Although his biggest problem is this other witness that claims he ran a red.