I totally agree with people like Matthew de Seattle. I am willing to bet your son has left out some details, or have changed some in his recount to you. It sounds more like your son went into the off ramp (after speeding on the straight away) with WAY too much speed, lacking experience, driving ability, and overdriving the car as he did, he was unable to avoid understeering right off the road, at which point, he went into the shoulder, then the barrier.

If I were you, I would have a sit down with him and have a heart to heart with him. Not so much as to get evidence to throttle him, but just to get the truth as to what really happened.

I once hit a dead skunk at over 120km/h on a dark stretch of highway. The impact was so violent, I swore something must've been damaged. I stopped as soon as I could, and looked for damage with a torch light. Nothing at all beyond some fur. I hit the skunk so darned hard the whole side of the car got air born, yet I sustained no damage to the car whatsoever.