I know some of these men are quite abnormal and inhuman but to say they just hit your brother when he did nothing means the officer must be very mad.
Are you sure they didnt exchange some words first? Even if it was in explanation of some things?
What did your brother alight from the car for? To open the boot? Present his papers? Or were they trying to search him? What warranted his coming down from the vehicle? I hope he didnt come down to scream at the policeman or swing his fingers in his face?
See, dear Nigerians, a good percentage of Nigerian policemen are not normal, so when you meet them on the highway, just be calm, some of them need reasons to fire their guns..let it not be you.