How does Cobbet... (spoiler)
...equipped with the fatal bullet, find Carleton's sister, since everybody else who seeks her has to be tipped off by crooks in the know that her apartment is identified as occupied by "Caldwell"? Prison records might show that Carleton had next-of-kin, but those records would not likely reveal that his sister's premises were deliberately misidentified.
How does Horace McCoy's novel handle this?
P.S. Did this role prepare Kenneth Tobey for hunting down a sadistic super-carrot? (Just kidding. ;)