Ten registered offenders live within 1 mile of Somer's school, Grove Park Elementary, a 10-minute walk from her home.
Finkelhor said sex offenders tend to have lower recidivism rates than other felons, and many of the worst crimes are committed by first-time offenders. However, he said, it's well worth law enforcement officials' time to interview offenders who have a history of crimes against children.
"One of the best and most important uses of registries is as tool of law enforcement, so they can identify individuals who have committed similar crimes. It is important to check those people out."
The search for Somer entered its third day Wednesday, as hundreds of local, state and federal authorities scoured the area around which the second grader was last seen.
With no physical evidence and no leads, police are hoping the interviews might help in the search for Thompson, who ran ahead of her friends and siblings while making the short walk home from her elementary school around 3 p.m. Monday.
"This case is very troubling in that we just don't have a lot of information," Clay County Sheriff Rick Beseler told "Good Morning America," adding, "We really believe that ... Somer has been removed from the area."