anchor: The way I reason is this: as a last chance they'll let Jane Finn escape in the hope that she's been shamming this memory stunt, and that once she thinks she's free she'll go right away to the cache.
positive: They hope that, if she's faking, she'll lead them right to the cache.
negative: They're letting Jane Finn go because they think she's telling the truth and doesn't know where the cache is.