FORT LAUDERDALE, Fla. (NewsNation Now) — FBI Agent Daniel Alfin gained international attention when he led a team that shutdown a major worldwide child pornography website. Agent Laura Schwartzenberger worked more anonymously, teaching children and adults how to avoid online sexual exploitation.

Alfin and Schwartzenberger, who were gunned down Tuesday while serving a search warrant at a child pornography suspect’s South Florida apartment, devoted their careers to capturing criminals who sexually abuse youngsters, often times testing the legal boundaries of computer privacy.

“We are still reeling from the news,” said Shelley Allwang, director of the Exploited Children Division at National Center for Missing & Exploited Children. “I feel lucky to have worked with people who had such commitment and resolve.”

The suspect was identified Wednesday as 55-year-old David Huber, who lived at the apartment complex. A law enforcement official familiar with the matter said investigators are looking into whether Huber may have been using a camera to monitor the agents’ activity before opening fire on them and believe multiple shots were fired through a door. The official could not discuss an ongoing investigation publicly and spoke to The Associated Press on condition of anonymity.

Three other agents were wounded, with two of them hospitalized. Both of the hospitalized agents were released Wednesday. The third agent was treated at the scene. Huber apparently killed himself after a standoff.

Florida court records show Huber with only minor traffic violations. He had no listing as a sex offender and no Florida prison record. Records show he owned computer consulting businesses from 2008 until last year. Broward County records show he was divorced in 2016.

Alfin, 36, and an agent for almost 13 years, made headlines seven years ago when he led a team that took down a Naples, Florida, man who was the lead administrator of Playpen, the world’s largest-known child pornography website. Steven Chase had created the website on Tor, an open network on the internet where users could communicate anonymously through “hidden service” websites.

Playpen had more than 150,000 users worldwide. Members uploaded and viewed tens of thousands of graphic images of young victims, categorized by age, sex and type of sexual activity involved. The FBI launched an investigation in 2014 after Playpen’s IP address was accidentally revealed.

After Chase’s arrest in 2015, the FBI kept the website operating for two weeks to identify other users, hiding malware in the images to discover their IP addresses. From that effort, investigators sent more than 1,000 leads to FBI field offices across the country and thousands more to overseas law enforcement agencies.

According to the FBI, 350 arrests were made in the U.S. and 548 internationally, including 25 producers of child pornography and 51 abusers. The operation identified or rescued 55 American children who were sexually abused and 296 internationally. Chase got 30 years.

“It’s the same with any criminal violations: As they get smarter, we adapt; we find them,” Alfin said at the time. The New York native added, “It’s a cat-and-mouse game, except it’s not a game. Kids are being abused, and it’s our job to stop that.” He was married and had one child.

Allwang, who worked with Alfin on the Playpen investigation, said he was humble, collaborative and committed to the mission of stopping child exploitation.

“Dan was unwavering and had steadfast resolve to try and locate and rescue as many children that were being abused as he could,” Allwang said. “It was never about ego or credit or anything like that. He was just a really selfless and collaborative individual.”

Schwartzenberger, 43, and an agent for 15 years, was part of Rockway Middle School’s law studies magnet program, teaching children about the internet’s dangers, including sexual exploitation and cyberbullying.

“She would always say, ‘I feel that coming here and talking about the hard stuff means that I won’t see you guys on my end,'” the Miami school said about the Pueblo, Colorado, native in a statement.

Allwang said Schwartzenberger was “a wonderful collaborator,” who always shared any information about her cases that could be helpful to the center.

“Laura was committed to seeing that through and to get that information entered in so those children could be helped,” Allwang said.

Attempts to reach the agents’ families Wednesday were not immediately successful.

“Our hearts are filled with concern and grief about the FBI agents who lost their lives or were wounded in the line of duty today in south Florida,” United States attorney Lawrence Keefe said after the shooting. “All of us in local, state, and federal law enforcement recognize and honor the daily risk taken by the brave women and men who dedicate themselves to keeping the public safe. This tragic incident is especially heart-wrenching as it affects our U.S. Department of Justice family here in Florida. Our thoughts and prayers are with the agents, their loved ones, and their colleagues on this most difficult day.”