Everyone who enters the US is photographed and fingerprinted (e.g. tourists, visitors, etc). Everyone who applies for a US visa is additionally photographed an

Everyone who enters the US is photographed and fingerprinted (e.g. tourists, visitors, etc). Everyone who applies for a US visa is additionally photographed and fingerprinted. Everyone who applies for naturalisation is additionally photographed and fingerprinted. The suspects did all three of these things. The US government has almost every foreigner legally on American soil in a database. Plus then you have the DNV on top of that and or passport office.