Neil, a 32-year-old Canadian who has been a teacher in Thailand, South Korea and Vietnam, is accused of having sex with at least a dozen Cambodian and Vietnamese boys, some as young as 6.
Border guards in Thailand and neighboring countries were on alert in case Neil tried to leave Thailand. Cameras at the immigration counter captured him Oct. 11 as he arrived at Bangkok's international airport from South Korea.
"We are quite certain he is still in Thailand and we think we are moving closer," Thai police Col. Apichart Suribunya said Wednesday. "Even if he uses a fake passport to try to get out of the country, his pictures are already published everywhere."
The hunt for Neil began three years ago when German police discovered about 200 online photographs of a man sexually abusing children. His face was digitally obscured, but German police were able to reconstruct a recognizable image of the man who has eluded police for years.
He was identified with the help of hundreds of tips from people who responded to an unprecedented appeal by Interpol for public assistance.
The photo of Neil arriving in Bangkok was broadcast around the world Tuesday when Interpol and Thai police named him as their suspect.
"We are trying to gather enough evidence of what he did in order to ask for the issuance of an arrest warrant from a Thai court," said Apichart, who is coordinating the Thai investigation.
"We are also trying to find more information and investigate his connections in Thailand that he made during his previous stay so we can get closer to him and his network of friends and help," he added. "We want to find this man as soon as possible to prevent him from abusing Thai children and other children."
Although there was no clear progress in the search for Neil, more clues about his background emerged with the discovery of a page on the social networking Web site MySpace apparently created by Neil. Interpol officials said they believe the page was kept by Neil.
"Been kicking around Asia for the past five years, teaching mainly and finding other forms of mischief," read the profile, which also described him as "5 feet, 11 inches tall, slim and slender."
"I love teaching, can't get enough of it really," the entry says, going on to describe his passion for drama, musicals and karaoke.
Separately, friends described Neil as outgoing and fun to be around. Co-workers gave mixed reviews of his teaching skills, but all described a man they believed to be harmless.
Former colleagues in South Korea said he arrived in August to teach at the Gwangju school, a small international school in the city of Gwangju, 370 kilometers (230 miles) southwest of Seoul. He failed to show up for work last Thursday - the day he flew to Bangkok on a one-way, full-fare ticket, according to Interpol.
"He was a very good teacher ... His kids really liked him," said Ray Fowler, a Canadian teacher at the school who said he lived next door to Neil. He said Neil taught social studies and English to grades seven and eight.
It was a different story in Thailand. Poramit Srikureja, an assistant chairman at Ramkhamhaeng Advent International School in Bangkok said Neil didn't pass probation at that school because of sloppy lesson plans and instances where he left students unsupervised in the classroom.
Both schools said there were no complaints of abuse by parents or students during the time he was at the school.
Before teaching in Asia, Neil had worked as a chaplain in Canada, counseling teens.
Neil will be extradited to Canada once he is arrested, said Kim Scanlan of the Toronto police child exploitation unit. Canada's sex tourism laws allow prosecution for crimes committed abroad.