Alexis says her three nines lost to Castle's three Jacks on the river but one of his hole cards is not a Jack. There can't be two jacks on the board because then Alexis would have a full house.
The phone's "SIM card" that Ryan puts into the computer is actually a micro SD card.
Demming, Thornton and Esposito all worked at the 54th precinct at the same time (Esposito transferred immediately after Thornton went missing, and they all have the key chain). Demming should be well aware of a cop from his precinct going rogue and then seemingly getting killed. In addition, a picture of the mysterious piece of metal is shown on the "war board" and both Demming and Esposito have every chance to see a picture of something they carried on their keys every day.