Game Of Thrones Season 7: 7 Things You Might've Missed In 'The Queen's Justice'
4. Maester Luwin's Scrolls
According to Maester Wolkan, his predecessor at Winterfell, Luwin, kept records of every scroll he received during his tenure at Winterfell. It may not sound like an important detail, but it certainly gets a reaction out of Littlefinger, who immediately looks intrigued about it.
We're gradually building to Littlefinger making his real play for Sansa, rather than just the little whispers, and this could be a part of it. There aren't too many letters we know of, at least in Luwin's time. The most notable ones are from Lysa, stating she believes the Lannisters murdered her husband, and one from Sansa, forced by Cersei, advising Robb to bend the knee.
On the surface, the former doesn't implicate Baelish (we also saw that letter burned, though it is possible Luwin noted down its contents afterwards). However, just before Lysa dies, she says that she lied and killed for Petyr. If Sansa remembers that, and sees Baelish attempting to destroy the record about Jon Arryn's death, she could find that 2+2 = Littlefinger being at fault for this whole sorry game.
The other letter doesn't reflect well on Sansa, but she was just a young girl, and it was dismissed by Luwin as being Cersei's work. Could he hold that over her regardless? It's not a stretch to imagine Littlefinger trying that, or maybe he'll just go looking through the records for something to use as leverage, unsure of what's actually there.
Speaking of Littlefinger's crimes, he does avoid any culpability for another murder here. In Season 5, Olenna said to Baelish: "Together, we murdered a king. If my house should fall, I will have nothing to hide." And yet here her house falls, but she neglects to mention his role his things. Maybe it's because it's in the heat of the moment, but also there's the fact she wants to hurt Cersei personally, and not share the glory/blame.