When I worked in risk management for KPMG, we would often work for the serious fraud office on big assignments.

Remember the name Nick Leeson? The rogue trader based in Singapore that caused the collapse of Baring Bros bank (personal bankers to our Queen)
Here is a reminder
http://www.nickleeson.com/

The Baring security tapes were digital, pioneering in those days, something like 1 frame per second.
A team of us had to go through 3 weeks of tapes from maybe a dozen cameras to try and catch the couple of examples of him forging signatures. Couldn't 'fast forward' that much as there was audio (mostly telephone) to go with it.

It took about 6 months to gather sufficient evidence as the 1 frame per second was often inconclusive. Regular tapes would have cut the time to a fraction.