RegWaters,
I'm very sorry to hear about the accident. Our thoughts are with your FatherInLaw's Friend AND you FatherInLaw. Often the injured victim is only one who gets any attention, the other victim, the one who witnessed such an incident is ignored. Don't forget that your FatherInLaw can be injured by this as well.
You might want to do some websearches on Critical Incidents. Both men are likely to have to deal with mental issues of the accident. They might have flashbacks, insomnia, loss of appetite, etc., that can happen after an accident. It might help if they or their family are aware of these reactions.
I know this will further ingrain safety issues into my actions.
Good Luck...
Dan McCarty