THEY grabbed another pair of sex offenders down South this week, but not before they allegedly killed a young girl.

On Monday, investigators recovered the body of 5-year-old Shaniya Davis in a wooded area near Sanford, N.C.

Shaniya disappeared last Tuesday morning. Mario Andrette McNeill, seen with Shaniya on a hotel surveillance tape hours after her disappearance, was charged with the girl's kidnapping. Her mother, Antoinette Davis, was charged on Saturday with human trafficking and offering her daughter "with the intent that she be held in sexual servitude."

Good thing the perps are always south of the Mason-Dixon.

Or are they?

Buried in last month's New York Times coverage of 7-year-old Renee Thompson's murder in Florida was a reference to police having interviewed the 161 registered sex offenders who live within five miles of the girl's home. (One hundred sixty-one?) Subsequent reports noted that all 161 had been interviewed and found to be uninvolved in Thompson's disappearance and murder.

Still, the number of registered offenders staggered me. More evidence that if you're in Florida and can't see the water, you're in trouble, I thought. And a damn good thing that number doesn't reflect the situation out on the leafy Main Line, I thought.

But I was wrong. It took just a few minutes of online investigation to open my eyes to the environment in which my wife and I are raising three young sons.

Consider the 5 foot 11 inch white male who lives on Apple Street in West Conshohocken. Or the 5 foot 9 inch man with brown hair and eyes who makes his home on East Hector Street in Conshohocken. Or the 6 foot, 190-pound white male on Jones Road in Gulph Mills.

Each of these men lives within a few miles of my home. All are listed on Pennsylvania's Megan's Law Web site. Which means anybody with an Internet connection is a couple of clicks away from knowing their addresses, birthdays, tattoos or other identifying marks, as well as the make, model and license-plate numbers of their cars.

Not to mention the crimes for which they were convicted. One committed aggravated indecent assault on June 20, 2002. Another was convicted of aggravated indecent assault on Jan. 26, 1994. The third was found guilty of unlawful contact or communication with a minor on Sept. 5, 2007.

Pennsylvania's Megan's Law Web site reports that 373 registered sex offenders live in Montgomery County alone. And when I entered my home address into the national search engine at FamilyWatchdog.us, I found that 137 registered offenders live or work within seven miles of my house. The Megan's Law site, meanwhile, identifies 1,654 registered offenders in Philadelphia.

Ernie Allen, president of the National Center for Missing and Exploited Children, confirmed for me that this is far more than a Dixie issue. At last count, he said, there were 686,515 registered sex offenders in the United States - up threefold over the last decade. Even worse, at least 100,000 of them are currently not complying with their registration responsibilities.

"The reality is this is a problem in every state, and people need to be vigilant and aware. It's important that they not overreact to it. But I had a mother of a victimized child say to me once, 'If there's a dog on my street that has the propensity to bite children, has a history of biting children, I want to know about it,' " Allen told me.

His point about overreacting is an important one.

"All sex offenders are not alike," he said, and not everyone listed on state or federal Web sites are guilty of the most dangerous crimes. "But, nonetheless, in order to get into that database, you have to have been arrested, charged and convicted of a prescribed sex offense."

Allen's advice? Access the information available. Talk about it with your kids. Use common sense when assessing the local risk. "Vigilance is what you can do with that information," he said.

AS I PREPARED to hit the "send" key to submit this column, I took yet another look at the Megan's Law Web site.

This time I entered the ZIP code for the North Broad Street building that houses the Inquirer and the Daily News, the receiving end of my column-filing. I found that 26 sex offenders live or work in the area immediately surrounding Broad Street's famous white tower. Twenty-six!

More proof that vigilance shouldn't be limited to summer vacations in the Sunshine State.

Listen to Michael Smerconish weekdays 5-9 a.m. on the Big Talker, 1210/AM. Read him Sundays in the Inquirer. Contact him via the Web at www.smerconish.com.