In most cases they are people you or your children know.
They are people you thought you could trust.
As one expert explained, some of them are not as bad as you fear, and some are worse than you'll ever know.
One sex offender on probation in Westchester County is failing a polygraph test, for the second time.
The polygraph shows he's had multiple victims, and officers suspect one may have been his daughter.
He then got the bad news from the polygrapher and his probation officer.
Polygraphs are relatively new in sex offender treatment.
Westchester's program also includes mandatory group therapy.
There's also intense supervision, Eyewitness News followed along as probation officers visited a level 2 registered sex offender.
A lot had been made of the levels which range from 1 to 3.
1 is considered low risk, 2 is moderate risk and 3 high risk.
"If there's someone in your neighborhood who you know is a level 3 sex offender, you know he's pretty bad guy," said Rory Bellantoni, a former Westchester judge.
Level 3's and 2's are listed on the online state registry, which you can check, but not level 1's.
Only police departments know about them.
The levels are determined by a judge in the sex offender court right after sentencing.
It's based on a point system that considers factors such as use of violence and the age of the victim.
But those levels don't tell the whole story.
You can have a level one sex offender or even someone who isn't required to be listed as dangerous who is very dangerous, and you will never know about them.
"To me, the scariest are the ones that you don't know about," said Westchester probation officer, Veronica Glueck.
"You find out they have 50, a hundred victims and no one knows," said Jerry Kiely, a Westchester probation officer.
The truth usually only comes out in time, long after the court process, through confidential treatment where additional crimes cannot come back to haunt them.
"The average number of victims that these folks have had is 54 before they got caught this time," explained Westchester Probation Commissioner, Rocco Pozzi.
Eyewitness News had a conversation with a level 1 sex offender.
EWN: you are charged with one victim."
Sex Offender: "I was charged with one victim. Correct."
EWN: "But, there were others."
Sex Offender: "I had other victims. I had 19 other victims in total."
EWN: "That you were never charged with?"
Sex Offender: "That I was never charged with."
EWN: "You would estimate that there were now many underage girls?"
Sex Offender: "About ten. About ten girls."
EWN: "And you knew they were underage?
Sex Offender: "Yes. I knew their age."
EWN: "I'm just curious, did you know that what you were doing was wrong?"
Sex Offender: "Yes, I will not pay for those crimes. Correct. That's something that they're going to have to live with."
He, like many of the sex offenders in Westchester, will be monitored by probation and mandatory treatment for 10 years.
"If I wasn't in treatment I would continue to reoffend. Absolutely," said the Sex Offender.
"Do you think you should be charged for the other victims?" asked Eyewitness News.
"I mean I'm guilty of them. I mean I acknowledge that I'm guilty of it. I mean I know what I did was wrong and I know that I did what I did," said the Sex Offender.
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