Was a police report filed? If so, he should contact the police and obtain a copy of the report.
In an incident I was in many years ago, I got a copy of the report and found many inaccuracies and omissions. The sorts of omissions that could be the difference between following up on something as an assault and merely another bike accident.
When I called back to amend the report that had been filed, the officer said “We’re not going to catch the guys so why do you care?” The only way to combat this apathy is to keep bringing it up until it is done right.