For thousands of hours the 49-year-old assumed fictitious identities of young people on the internet - and has spent more time being a teenager online than any real teenager.
His work meant numerous adults were arrested for trying to prey on children, mostly in Australia but also in joint operations with NZ police.
Each day Mr Lee's online identities would be approached by dozens of potential offenders, and he would choose those he felt were most dangerous to talk with.
One used encryption software to hide his identity, but, like the rest, was traced and caught.
"The internet provided an environment they'd never had an opportunity to have before and they had access to thousands of children under what they thought was a cloak of invisibility," Mr Lee said. "The screen is brilliant at giving a feeling of anonymity ... that's why a lot of people make choices online that they wouldn't make in the real world."
Mr Lee spoke to the Weekend Herald yesterday before talking to Year 7 and 8 pupils (11- and 12-year-olds) at Diocesan School for Girls on online safety and cyberbullying.
A false sense of anonymity and disconnect from real world sensibilities contributed to both problems, Mr Lee said, and realising that went a way to safeguarding children and teens.
"A young child sends a threatening email to another child. The only thing they're going to imagine is the child reading it, not the hundreds of other scenarios that could cause their anonymity to be undone."
Diocesan principal Heather McRae said the school wanted to take a lead on addressing cyber safety and bullying, as issues often became apparent at school before the home. "[Teenagers] are so vulnerable in the years that they are putting together their self-identity and who they are.
"And some of the more vulnerable ones do seek that external feedback, but of course the internet is such a random and unmonitored place ... and it is an unmitigated disaster for students who are very sensitive."
Mr Lee, who has also worked with the FBI and Department of Homeland Security Cyber Crimes Centre in the United States, said online safety had improved in many ways, and that six years ago the definition of cyberbullying was largely unknown.
He has four children aged between 10 and 19 and laughed when asked if they were allowed to be online.
"They are, whether I want them to be or not, they would be there. I appreciate that even with what I've seen, the internet is a very positive environment. It just reflects the real world."
But there is also a greater need for vigilance. A survey revealed 73 per cent of Year 7s and 8s at Diocesan had their own smartphone. The school is private, but the tumbling price of such technology meant it was becoming more popular with young people from all backgrounds, Mr Lee said.
"Back in 2001 everyone in the family used the one computer, no kids had computers in their bedrooms. The technological factors are making the education more important now."
