There are plenty of databases out there that can be interrogated.
It's a question of authorisation to do it.
I've done this myself and it's quite labour intensive even when the ID of the person is known and is correct.
If there are various 'indentifiers' it starts to get more dificult, but still possible. However, access to some pretty confidential databases are needed. That would be my only concern.
I would imagine most of these people are deliberately keeping themselves below the radar and in these cases I don't think they will be found from computer analysis alone. Feet on the street will be needed.
