I would suspect it was a classic case of a ringleader or two, and the remainder coerced into going along with it.
This is why anti-fraud measures protect not only the company and the public but also employees. If fraud is difficult (its never impossible) then temptation and the possibility of staff being coerced, pressured or cajoled into it, by colleagues or others, is much reduced. Plus if fraud DOES occur, if its impossible for you to have done it you get ruled out earlier and have a less stressful life.
Its also why 'trivial fraud' (like Stationary Theft) is stamped on. Trivial fraud gives those that know about it a toehold to coerce or pressure you into 'slightly less trivial' stuff and eventually progress into serious fraud.
Its a good policy in situations where a group of people handle money to rotate staff in and out - it makes it harder to set up and maintain a 'group fraud' and hopefully breaks up or prevents a 'fraudulent culture'. Few would go as far as one manager I know of who randomly selected his cash office staff from a large pool on a daily basis and imposed a 'two people or no people' rule wherever cash was being dealt with.