You may be right.

My logic is this: These devices are capable of providing a piece of evidence in a potential criminal prosecution. If the computer detects no anomaly, then it has decided there is no potential evidence and the data goes away. If it does detect an anomaly, it should at least keep the data required to construct the image until it is no longer a potential bit of evidence. To do otherwise would be nonsensical from a law enforcement perspective and I would expect it. When I am cleared, I also expect the bits and bytes to go to their cyber graveyard somewhere.