They use a system derived from the legacy TECS (Treasury Enforcement Computer System) system. I Once the passport is scanned it check the person's biographical data, passport numbers, ect. against all law enforcement data bases. When a passenger checks in for their flight at a foreign destination, the air carrier transmit that information via APIS (Advanced passenger Information System) Basically, everyone on your aircraft is being checked even before your aircraft touches down in the U.S..
If there are "issues", you are sent to a Secondary Inspection Office so the Officer can fully look at records dealing with the issue. The Officers in the Booth only see your bio info and confirm you on the arriving flight. They cannot see how many parking tickets you had. And it's a BIG no no to show the arriving passengers the screen they are looking at.