The first time Capt. Rhett McQuiston had to look at child pornography, he vomited.

"I threw up in a trash can, and I had to go home," he said. "I stayed up all night thinking, could I do this job for even the two years I signed on to do it?"

To fight online child pornography, Utah's Internet Crimes Against Children agents have to witness it. They view the images for about 20 hours of their 50-hour work week, searching for clues about who made it, who has it and where the victimized child might be.

During the past 10 years, McQuiston, 39, became the longest-serving ICAC agent in Utah, and made more Internet child sex offender arrests than any other officer in the country, said Utah Attorney General Mark Shurtleff, whose office oversees the unit.

Friday was McQuiston's last day as head of the unit.

"He's done some very difficult, amazing work," Shurtleff said. "It's simply amazing he has lasted this long."

When he started with ICAC, McQuiston was 29 years old, with a baby daughter at home. He came to the unit from Adult Probation and Parole where he monitored sex offenders online after their release from prison. He'd started training in the Internet crime field in 1997, when it was still new and home computers were relatively uncommon.

Now, offenders might have a desktop computer, two or three laptops and cell phones, he said.

"The number of investigations have just gone through the roof," he said. Arrests have increased by double-digit percentage points every year, and since 2007 they've gone up 60 percent, he said.

"The problems have been around as long as mankind," he said. "Technology ... allows [offenders] to feel more safe, staying at home on their computer."

It has also made it easier and cheaper to record children being victimized. As the amount of crime has grown, so has the task force. From four agents at the start, the task force has grown to eight agents, two analysts and 13 part-time people.

But the work doesn't get any easier.

"For me, it was the sound of children being raped and abused" on online videos, he said. "But you have to listen to it because you pick up clues."

To help officers deal with the disturbing images, McQuiston and the captains before him have kept the atmosphere casual, calling each other by their first names and playing music. Agents take frequent breaks and often work out.

For his part, McQuiston often mutters under his breath, sometimes using unprintable words.

As difficult as it is, the payoff, he said, is that unlike other police work, the task force work can prevent abuse from happening. In typical abuse cases, it can be years before a childhood abuse victim can come forward and report the abuse, often long after the evidence is gone.

"I do believe in stopping someone early on. Some child out there is going to grow up and not have some of those emotional scars," he said. For parents, he said, the best way to prevent abuse is open communication, especially online. While many parents keep close tabs on where their children are, some aren't as vigilant about their Internet activity.

McQuiston now has two children, a son and a daughter, but he didn't have a computer at home until last Christmas, when his wife convinced him the children would need it for school.

"I'm not saying that's the right way to go," he said, but after spending his day on the dark side of the Internet, he didn't want to be online at home.

On Monday, he'll start his new job on a new attorney general's task force, focusing on undocumented immigrants who commit violent crimes.

"I'm very proud of the work we've accomplished as a team here," he said, but "I hope I've seen my last child pornography."

lwhitehurst@sltrib.com