Besides, Robb was already preparing to lead House Stark's soldiers north ahead of the others. This battle at the Wall would give him another chance to unite all the North's forces and consolidate his power.
If this Stark of dubious legitimacy were removed during that time, even if Roose Bolton really were responsible, it would not stir up further conflict across the North. Instead, it would make them more hostile toward House Bolton and more loyal to Robb, the new Warden of the North.
But Jon knew nothing of any of this. As he saw it, since Roose Bolton had agreed to answer Robb's call to arms, and Jon himself would be marching with the Dreadfort's forces, he had to make sure this task was done properly for Robb.
Only Jon knew that the thin letter buried beneath the pile of documents now weighed heavily on his heart, constantly reminding him that Stark blood still flowed through his veins.
Ramsay had been watching Jon, hoping to see his reaction after receiving the letter. Unfortunately, their relationship was strained now, and he had no chance to enter Jon's room again.
So the next day, he approached the old Steward, Edgar, and asked him to send a letter to Winterfell by the fastest Raven route, without submitting it to his father, Earl Roose, for review.
The letter contained only a few lines: Jon Snow is on very good terms with Ramsay, House Bolton's heir, and he wishes to contact those of us planted in the Dreadfort in secret. I suspect his loyalties have shifted, which could threaten House Stark. I recommend keeping a close watch on him.
Ramsay did not sign his name. He simply sealed the letter with the House Stark Direwolf stamp he had just prepared.
A Raven flew out