I dont think an insider is implicated here...i think what they had descovered is a small glitch wih would allow machine deposits to be cleared without human verification (hence the carrying out of the plan over the long christmas week end.) depost checks and draw the money the next day - i remeber back in the 80's you were able to do that at royal bank in canada

or maybe they deposited checks to these accounts on christmas eave and the checks were not held..den wthdraw money all weekend.