Replying to need help, comp experts

my friend is in some trouble with the law and they are most likely going to check out his computer. i need a very good nuker virus that will destroy, cookies, files logs, and especially AOL conversations (which if they found them would just incriminate even more people.)
would deleting cookies stave off the law from reading his conversations? or am i going to need to go further and have to find a virus (nuker/flooder?) that will crash his computer so they can't find anything. this is not a joke. any direction helpful.
-AndrewP
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Go Fishing. Go Ride.