But the weird thing is, based on Gil's route day 7, Walter and Herbert became distant after the accident. Maybe neither Walter nor Herbert doesn't want to take responsibility for the accident?
And how in Mark's episode, he saw someone who looked like Walter even before Walter came to Highwell. Maybe Herbert knew their childhood friends now live Highwell (especially at Highwell University) and somehow convinced Walter's parents to let Walter move out to Highwell to make Walter remember the accident?
edit: minor Gil's day 8 spoiler down below
This could explain the hooded figure on Gil's day 8, "This voice, is it really him??". Maybe it's Herbert trying to spy on Walter in case he remembers anything and takes the blame on Walter?
(again all of this is a wild guess lmao)