Unfortunately the plot twist of ESB casts Ben’s motives and statements in ANH into an entirely different light than what was originally said, shot and intended.
But if you look at the original film without any connection to the sequels it is merely that there is some sort of story there that Ben harbors some guilt or emotional weight over and this must have either been a direction given, or something Guinness picked up on and either did on his own or very likely asked George. I’d say that originally it would be like any child asking how a parent died who had done so unjustly-and your response would have to be carefully crafted and spoken whilst bringing up painful memories.
It is unfortunate that the sequels have undone parts of Obi-wan’s characterization and thus became the standard lore.
I do think that Alec’s performance is so full of delicate intricacies and is agonizingly underappreciated. He later regretted the sheer amount of attention he got over this one role but it’s really a masterful performance-even in a career peppered with ones that define the craft itself. As a huge Guinness fan, I always find myself remarking at just how developed his role is past what is on the script page. It really is one of his truly great roles and is the one thing that really carries the film in terms of being the central strength for everything to work from. The inspired part in casting was not simply finding a name star but to approaching a master well known for finding character intricacies and then making each part feel as if it were lived in.
My only regret is that Tarkin is not given more screentime and that we didn’t get a confrontation with Alec and Peter Cushing getting to work together.
That said, I do think Alec would have likely done a few things a bit differently had Obi-Wan’s fate been decided earlier on.