Oct. 21, 2009 -- There are so many sex offenders living within blocks of where 7-year-old Somer Thompson vanished Monday that when their homes are represented by pins on a digital map they create a cluster so thick it overlaps in places.
Law enforcement officials have interviewed at least 75 registered sex offenders who live within a 5-mile radius of the second grader's home on Orange Park, Fla., but state officials say there are some 161 convicted offenders in that area.
Experts say despite what appears to be an extraordinary concentration, the number of local offenders is actually quite typical for an area so close to a major city. Most people, they say, have no idea just how many sex offenders are living in their neighborhood.
"In spite of appearing it to be a lot, that's about average," said Ron Book, a Florida lawyer who lobbies for tougher sex-offender legislation. "Some areas have hundreds of offenders."
According to the Florida Department of Law Enforcement, which maintains the state's sex offender registry, there are some 82 sex offenders living with a 3-mile radius of Somer's home in Orange Park, a suburb of Jacksonville, and 161 registered offenders within a 5 mile radius.
By contrast there are 10 McDonald's restaurants in the same 5 mile radius.
State officials would not comment on whether they believed 161 offenders in the area was a high or moderate density.
But Professor David Finkelhor, director of the Crimes against Children Research Center at the University of New Hampshire, agreed that 161 sex offenders in a 5-mile area that included parts of a major city is not necessarily a high density.
"Different states have different policies about what level of sex offenders are required to register. You can have over 1,000 offenders in an urban area without much difficulty. It sounds scary to people, but many states have registration regimes that include people who are not all that dangerous," he said.
The 5-mile radius around Somer's home in 1700 block of Horton Dr. in Orange Park includes parts of the city of Jacksonville, the largest and most populous city in Florida.
There are some 53,201 registered sex offenders in the entire state of Florida. Of those, 318 live in Clay County, where Orange Park is located and an additional 1,671 live in Duvall County, where Jacksonville is located.
The ratio of residents to sex offenders in Jacksonville is estimated at 486 to 1.
Of the 161 offenders in the area, 16 are classified as predators, which generally means the offender was convicted of a first-degree felony sex offense – many of which involve the molestation of children.
Laws about where sex offenders are allowed to live vary from county to county and depend on the severity and nature of the crime for which the criminal was convicted.
Book said sex offenders often cluster together in part because of laws that restrict the places in which they can live.
Though high concentrations of offenders appear to be problematic, high densities actually help police.
"Some laws have forced clustering. While that appears to have a downside, some say it's a good thing from a law enforcement prospective. If you have clustering its easier for parole, probation and police officials to keep track of them," he said.
Some offenders are not permitted to live within 1,000 feet of a school or are banned from activities like distributing candy on Halloween, said Mike Morrison spokesman for the Florida Department of Law Enforcement.
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."