"The Whole Story," by Andrew Welsh-Huggins, in Black Cat Mystery Magazine, Issue 7, 2020.
This is the second appearance here by this author.
Hayes is a private eye with a strange assignment. Bobby Putnam is in prison for driving drunk, resulting in the death of his daughter. He doesn't deny the crime but he wants Hayes to confirm his impression that the driver whose truck he hit was not looking at him. His eyes, Putnam insists, were on a man across the street, man who vanished before the cops arrived.
Not that it would have changed Putnam's guilt. But he is desperate to know if he's right about this one niggling detail about the event that destroyed his life.
Of course there turns out to be more to this clever story.