When Darth Vader's ship captured the Tantive IV at the start of A New Hope, he tells an officer,
I have traced the rebel spies to her.
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How did Vader trace the rebel spies to Princess Leia?
I am looking for anything in canon sources that mentions specific spies whom are in contact with Leia. And please say how Vader knows the spies are in contact with Leia.
Edit to add:
Vader watched the Tantive IV depart at the end of Rogue One, but he says he traced the rebel spies to her instead of saying, "I just saw this ship flee Scarif with the stolen plans." Does he know of her rebel leanings from other sources besides merely being on the ship?
Just as Rogue One corrected inconsistencies in the original Star Wars movie (e.g. - one person said stolen data tapes and another said the ship intercepted transmissions) and filled in details (e.g. - the opening crawl of the original movie said the Rebel Alliance just won its first major battle), I would like to know if any canon sources provide details about rebel spies and their connections to Leia.