TORONTO — She is perhaps 12 now, her hair still light blond, but she doesn't smile anymore. Over the last three years, she has appeared in 200 explicit photos that have become highly coveted collectibles for pedophiles trolling the Internet. They have watched her grow up online — the hair getting longer, the look in her eyes growing more distant.

"She's a collector's item," says Det. Sgt. Paul Gillespie of the Toronto Sex Crimes Unit. "I know somebody out there could lead us to her. But right now, the only ones who can see her face are the wrong ones."

To his shame and frustration, all he could do was watch as the photos kept appearing and all the usual tricks to trace her failed. So he decided to try something different. A computer expert digitally erased the girl from the photos, and in February, Gillespie asked the public to help identify the locations: a hotel room, a fountain, an elevator and a video arcade.

Moments after the pictures appeared on a Toronto television station, the tips began to come, and caller after caller identified a Walt Disney World hotel in Florida. A scan of hotel records gave the police a few clues: They believe some of the pictures were taken by a relative on a family vacation and the rest of the photos were taken at a home.

Pushing boundaries

It was a rare breakthrough for Gillespie and his team at the Child Exploitation Section of the Sex Crimes Unit. A 25-year veteran of the Toronto Police Service, Gillespie has a willingness to push boundaries — including teaming up with Bill Gates to pioneer a tracking system that became available this month to any police unit investigating child porn.

But it hasn't been enough in the case of the Disney World girl. Now Gillespie wants to do something revolutionary and release a photo of her face. But aside from worrying that it would violate her privacy, he must weigh whether it would put her more at risk than letting the abuse continue while they search for other leads.

In another case, an abuser confessed to police that he'd been so certain that his victim's mother had figured out what was going on, he contracted with a fellow pedophile to kill her and the girl in exchange for more pictures and sex toys. What would happen if the offender saw the police broadcasting the Disney World girl's picture and knew he was going to be caught?

"Could harm be caused?" says Gillespie, 45. "Absolutely. Would it be more harm than would be caused for the rest of her life if we didn't do anything? We don't know. We're trying to determine the best thing to do."

Gillespie has been on that knife's edge since the Child Exploitation Section was created four years ago. The Toronto Police Service seized more than 2 million pictures and videos of child sexual abuse in 2003. So far, the world's law agencies have identified fewer than 500 children.

"We're doing a terrible job," he says in his office in Toronto's police headquarters. "Five hundred kids of 50,000? What is that?"

Their work is a daily sojourn to the underworld. Gillespie has a team of 10 men and six women who spend hours in front of their computers, extracting leads, writing warrants and sifting photos for clues. The payoff is the day they get to kick down a door and take "the bad guy" away. The mood is light and the humor often off-color to ease the horror.

On one wall is a Star Trek poster with investigators' faces substituted for the crew of the Starship Enterprise. But even that alludes to a dark fact of their work: All but one of the offenders they have arrested in the last four years was a hard-core Trekkie.

Detective Constable Warren Bulmer slips on a Klingon sash and shield confiscated in a recent raid. "It has something to do with a fantasy world where mutants and monsters have power and where the usual rules don't apply," he said. "But beyond that, I can't really explain it."

Role playing

And that is one of the biggest challenges of the work of the Child Exploitation Section. They need to get inside the minds of the victims and the perpetrators to find them, but there is only so far they can — or want to — go.

Sitting in front of two computers, Detective Constable Paul Krawczyk starts the day as a 13-year-old girl. Within minutes of entering a chat room on education, and without asking for them, men are e-mailing nude pictures.

By lunchtime, he is a pedophile conversing with a fellow "pedo" on the other side of the world about their shared interest. "R u active?" he asks, meaning, do you abuse kids. "Yea," the message comes back, "7 (years old) and 2."

The pedo describes his exploits in unprintable detail and eventually asks to exchange pictures. They negotiate for a while, and the other guy sends a dozen photos that seem to be culled from other Web sites.

Krawczyk says they will try to save any kid. But this guy is very far away, and none of the images seems to be the kind of homemade product of active exploitation.

Internet-savvy pedophiles have managed to stay steps ahead of investigators by using private networks, file-sharing software and surfing anonymously on public wireless systems.

Calling Bill Gates

Out of frustration one night in 2003, Gillespie e-mailed Gates, co-founder of Microsoft, asking for help creating a database that could combine information from around the United States — and the world — to help track down offenders and their victims.

AP This poster released by the Orange County (Fla.) Sheriff's office shows an image of a girl they believe may have a connection to another girl who has appeared in sexually graphic photos on the Web.

To his surprise, Gates responded, and after a year and a half of collaboration, Microsoft Canada and the Toronto Police unveiled the Child Exploitation Tracking System this month to help investigators share information.

The system is designed so that police in any country can plug into the system and cross-check data, including names, Internet aliases and the digital signature for every captured photograph.

"It's important, because when we see a new series of photos online, that child could be anywhere," Gillespie said. "We need to cooperate and not duplicate each other's work. We just traced a toddler to a particular neighborhood in Spain through a subway ticket in his picture."

Interpol sends Gillespie any photo series suspected to have originated in North America. Clothing styles, writing or even the shape of a wall socket offer clues to locale.

Gillespie hopes the tracking system will not only link the often overlapping investigations being conducted around the world, but that it will also save his team some heartache by letting the computers do some of the dirty work of sifting through the photos by their digital signatures.

"We arrested a bad guy last week," he said. "There were 1,000 images on his hard drive. Can I pay you enough to sit at this computer and look at every image? There are babies raped and sodomized with romantic music playing in the background. You are never the same person after you see something like that. It's soul-destroying."

The team is not allowed to send porn but can access new series of images the way college students swap music files. There are thousands to sort through, with new homemade images appearing every day.

"Sometimes you just want to take a shower after doing this," Krawczyk says. "Sometimes you want to throw the computer across the room. But when we do get a bad guy, it gives you great satisfaction. He wouldn't have been caught any other way."

Staying grounded

Almost every investigator in the office has a talisman to ward off the ghosts that haunt the workday. For Gillespie, it's a Christmas card from the mother of a 3-month-old boy who had been raped by his uncle, thanking Gillespie and encouraging him to keep going even when he wants to give up. Gillespie tells a bit of the child's story, then swivels his chair to face the window when his eyes begin to well up. He turns back, recomposed.

"I look at that sometimes," he says simply. "It makes me feel good."

They haven't been as fortunate in the case of the Disney World girl. Bill McGarry, a detective with expertise in graphic art, removed the girl's images from photos and digitally restored the scene. He enhanced tiny background objects to pick up on anything that could become a vital clue. Others on the team sent images of flowers and trees in some pictures to horticultural experts to help pinpoint the geographic area, and talked to brick manufacturers all over North America to glean clues from the wall in a photo. Anything. Everything.

As a result, they have narrowed the area down to the northeastern United States, and now the investigation is in the American authorities' hands. They have circulated sanitized photos in U.S. law-enforcement circles that specialize in missing children.

If that leads nowhere, Gillespie says, the investigators must turn to their last resort: showing the victim's face to the public for help.

"I know somebody out there knows her," he says.