My sister slipped and dislocated her shoulder at a local super store (Wegman's) about 3 weeks ago and we're attempting to get a copy of their surveillence tape as proof of the fall. This happened at the checkout counter, would that make a difference if they only video certain parts of a store? How long do these stores usually keep their tapes? And do they tape over them or what? Somebody told me that if they're digital they can keep them indefinitely. Thanks for your help.