It is important to keep in mind that even trained professionals, trained to observe and report, often fail to note or recall even the most basic facts about the details of incidents -- even when they are writing their reports within minutes of the incident's conclusion. They will be fuzzy about the time, who said exactly what and to whom, the date, even who was there. If it is a violent incident they often will not know for sure who hit whom, who grabbed whom, who was next to them and what they were doing, and they wont even necessarily know exactly what THEY did or said.
The reports, the memories, are a construct, a fiction that becomes the official history of the event once it's down on paper. This is not an indictment but a statement of fact -- it effects everyone. When it comes to remembering details, people suck.
What they are good at is remembering themes, emotions, the overall story. Somewhat. And this includes events that many would assume to be so traumatic and shocking that the details are branded in the person's memory forever. It doesn't happen that way though, and particularly with trainatic events.
This is, of course, the problem with witnesses. It is normal for witnesses to remember things that never occured, and forget huge things that did. The reason for this is that the memory of what actually happened was constructed after the fact, the details that were not noticed at the time were filled in later, and those new "memories" become locked in place.
It is entirely possible that step-dad remembers going to bed early. It is entirely possible that mom remembers him hanging on the porch with friends. It is also entirely possible, entirely possible, that a video recording of the home that evening would show that NEITHER description is close to accurate.
it's all over the place.
