That's the problem - how do you un-ring the bell? Once the competitor reads the information, even inadvertently, they know everything they need to know. Or if they claim they haven't read it - how could it be proven? To make matters worse, this is a competitor in a different state who is known to have considered opening an office here. They now have a very good handle on the potential revenues available to them ....
Of course, the "ex-employee" has a Non-Competition Agreement that specifically prohibits the sharing of any information.