Caffrey and Burke break a portion of a brick wall that leads into an old prohibition tunnel, destroying it in the process. However, the thief was supposed to have escaped through the same route just days earlier, somehow without damaging that same wall.
The way Caffrey "inspects" the diamond is very wrong. The diamond should be placed on a back-lit opaque glass and inspected from about 5-10cm (2-4") distance. He is holding it right into his eye, using a watchmaker's magnifying glass to do that.
The transcripts of the conversation between Neal and Peter misspell Neal's surname as "Cafferty" rather than "Caffrey".