1. Memories
When the trio decided to search R.A.B`s room for clues Harry didn't expect to find much, especially not letters clearly meant for his father.
While Hermionie checked the drawers and Ron checked the closet, he decided that, if he were to hide something, under the bed seemed to be the safest option. Apparently R.A.B had thought the same as he had hidden a fairly big box under his bed.
Now the three of them were huddled around said box, apart from the letters they discovered a leather journal (R.A.B was engraved on the cover) and a bunch of photographs.
“It seems like your father and R.A.B were close” Hermionie mentioned as she carefully flipped through the pages.
“Should we read the letters? Maybe there's something that might help us”
Ron agreed with Harry and they both turned to Hermionie who looked rather conflicted “It's not the most morally correct thing, is it? But I think it's worth a shot, we might find something useful”
“Even if we don't find anything you might learn something new about your dad” The red-head added.
So, with his friend's approval, Harry read the first letter. Luckily for them, they happened to be somewhat in order.