Annabel is aware of Jimmy’s past as a safecracker.
Explanation:
I’ve never read the book before, but I think this sounds like the most logical answer. Because if Agatha has a code problem, Jimmy’s past as a safecracker should help. Also, this answer is the most specific.
Ben Price recognizes that what the warden has told Valentine is true: "You're not a bad fellow at heart." Having observed Valentine's actions, the detective knows that Jimmy is in love and intends to "live straight." So, he grants the safe-cracker a reprieve, "a retrieved reformation."
