From Wiki:

At the Federal level, Megan’s Law is known as the Sexual Offender (Jacob Wetterling) Act of 1994, and requires persons convicted of sex crimes against children to notify local law enforcement of any change of address or employment after release from custody (prison or psychiatric facility). The notification requirement may be imposed for a fixed period of time - usually at least ten years - or permanently.

Running the guys license should have brought up his past. No?