I believe it is simply a matter of time, when he is at home some nurturing /kindness, support, quiet mind ,he will accept what happened to him eventually, is he left with any injuries? Give him time to remember , it can take quite a while but one day it is like a light going on and then he starts to heal from the trauma. all you can do is be there and supportive.If he gets depressed or cant cope then a visit to the Doctor would be a good idea.If he seems sad when you are with him suggest some distractions, maybe board games, music, reading I find Nature to be a great healer, sitting in a garden watching the birds in the sun, can be restoring. Good Luck let us know how he is doing.