The 4473's stay with the gun shop. The customer information doesn't get sent anywhere except for the NICS system. There is NO information about the gun except the type (long gun, hand gun, or other) that gets sent the the NICS. Interestingly the NICS is required by law to delete all evidence of the transaction within 24 hrs of 'resolution' (proceed/denied). That is why if you get repeated delays you can fill out some paperwork (VAF) which gives them permission to store data on you and they give you a unique ID number.
For multiple handgun sales (more than one within 5 days), the customer info along with information on the firearms (make, model, serial number) get's sent to the chief LEO in your jurisdiction. Might be the chief of police in a city, or a county sheriff if you live outside city limits. This info also gets faxed (and then mailed) to the Department of Justice and (I assume) is entered into the ATF's National Firarms Tracing center database.
http://www.atf.gov/publications/factshe ... enter.htmlMany border states also require a multiple long gun sale to be reported in the same manner.
I asked my ATF contact what the police do with the multi-handgun sales forms and she said "They probably throw them out because they don't know what to do with them. It's supposed to help solve local crimes but I've never heard of that happening. It doesn't matter what they do with it, but it's the law so you have to mail them the forms."
If the ATF wants to look at the 4473's as part of a compliance audit, they can do that at any time. If they are looking for information about a particular person/gun, I believe they need a warrant just like anyone else.