So, he told his mother he was going to see a friend and we're guessing this was before she went to work in the morning. He told her to drive safely, so this also sounds like she was leaving for work or somewhere, anyway, and it sounds like he was at home when they spoke. I'm finding this conversation odd because if he was talking about much later in the day, i.e. 8.45pm, that he was seeing his friend, you'd think his mum would therefore know that he wouldn't be home when she returned, and definitely wouldn't be sitting in his room when she went to tell him she was cooking dinner.
Incidentally, every room in my home (a 1st and 2nd floor flat in a converted London terraced house) had a lock each internal door when I moved in. I don't know how normal this is (the keys are standard 'Union' keys which all have a code on them and you can just buy replacements easily), but I don't find it odd that Richard's bedroom door was lockable or that he locked it when he went out. Privacy is more important to some people than others, I guess. As a teenager, I kept a diary, and I knew my mother would sneak into my room, locate and read it when I was out. If I'd had a way of locking my room, I definitely would have done so.
