Depending on the specific state in which the friend was convicted, the data may well be part of any number of commercial databases. More often than not, convictions (as opposed to arrests, conditional dismissals, and other odd bits) are public records and are trapped by routine services employed worldwide by business & government.

The specifics of this individual's conviction (and whether it remains) will matter.

One would hope that the worst the friend would face is being relegated to transit for 20 hours as the friend has an onwards connection, presumably to a place which won't deny entry.