MIAMI — The sun had not come up yet on Tuesday when a group of F.B.I. agents assigned to investigate criminals who prey on children online approached the Water Terrace apartments in Sunrise, Fla., to execute a search warrant, a routine part of the job that is always fraught with risk.
What exactly happened in the ensuing minutes is unknown, but a gun battle broke out, rousting neighbors out of bed in the quiet residential community. Law enforcement officials called emergency dispatchers. Multiple shots fired, they reported. Send air rescue.
Two F.B.I. agents died and three more were injured in one of the deadliest shootings in the bureau’s history. No agent had been shot and killed on duty since 2008. A similarly bloody shootout took place in a Miami suburb 35 years ago, killing two F.B.I. agents and injuring five others.
The man being investigated in the case, which the authorities said involved violent crimes against children, had barricaded himself inside the complex and was found dead. A law enforcement official said it appeared that the man had killed himself before agents were able to arrest him. His identity was not released until his family could be notified of his death.
Video footage from local police stations showed a grisly scene at the open-air apartment complex. A SWAT truck had rammed into staircase railings that lay on the ground in tatters. There were blood stains on the floor outside the apartments. The police swarmed to the complex, shutting down the roads and keeping people out for most of the day.
Christopher A. Wray, the F.B.I. director, identified the two agents who were killed as Special Agents Daniel Alfin and Laura Schwartzenberger.
“Every day, F.B.I. special agents put themselves in harm’s way to keep the American people safe,” Mr. Wray said in a statement. “Special Agent Alfin and Special Agent Schwartzenberger exemplified heroism today in defense of their country. The F.B.I. will always honor their ultimate sacrifice and will be forever grateful for their bravery.”
Ms. Schwartzenberger, 43, was a mother of two from Colorado and had been with the F.B.I. since 2005. She was part of the violent crimes against children squad in the bureau’s Miami field office, court records show. She was assigned to the Innocent Images National Initiative, a part of the F.B.I.’s cybercrimes program established to combat the proliferation of images of child sexual abuse online.
Mr. Alfin, 36, was a father of one from New York and had been a special agent since 2009. He was assigned to the Miami Child Exploitation task force. He discussed his role in an online F.B.I. article about the 2015 arrest of a Naples, Fla., man who ran what the bureau described as the world’s largest child pornography website. The site, called Playpen, had more than 150,000 users around the world.
“They put their lives on the line and that’s a hell of a price to pay,” President Biden said of the agents in remarks from the Oval Office. “My heart aches for the families.”
Dawn Garrick, a resident of the apartment complex where the shootings occurred, said she was awakened from her sleep shortly after 6 a.m. by blaring police sirens and cruiser lights gleaming into her ground-floor bedroom window. From her room, Ms. Garrick, 53, watched as concerned neighbors stepped out to see what was going on, only to be directed back inside by the police. About an hour later, she said, she saw paramedics loading someone on a stretcher into an ambulance.
The community is typically safe and quiet, she said.
“There are a lot of working professionals,” she said. “Everybody is friendly.”
Two of the wounded agents, each of them shot multiple times, according to the F.B.I., were transported to a hospital. The third did not require hospitalization.
The F.B.I. squads that investigate crimes against children are considered some of the most difficult assignments because of the disturbing and graphic nature of the cases they handle. Agents typically review horrendous depictions of children being sexually exploited, images that are then shared with others online.
Investigations into child sexual abuse often start with a tip from online social media companies like Facebook, which reported finding nearly 60 million images and videos in 2019 alone. About half of the content was not necessarily illegal, according to the company, and was reported to help law enforcement with investigations.
Yet companies can usually only detect a small percentage of what is distributed, since they rely on automated systems that can only flag material that has been previously flagged by users. From a tip of just one or two images or videos, investigators frequently find troves of thousands, or more, on a suspect’s hard drive.
The sharing of this imagery can also point to real-world abuse. It is not uncommon to find offenders who share child sexual abuse imagery who have also abused children in real life.
Mr. Alfin was involved in an investigation into a dark web forum beginning in 2014 where members would upload and trade graphic images of child sexual abuse. The investigation resulted in the arrest of at least 350 people in the United States and hundreds more around the world. It is credited with rescuing over 300 children, according to a news release from the F.B.I.
For the past decade, criminals have increasingly been using advanced technologies like the dark web — where users’ internet protocol addresses are obscured — to stay ahead of the police. In one case, an Ohio man helped run a dark website with nearly 30,000 members from 2012 to 2014. The site, now shuttered, required users to share images of abuse to maintain good standing, according to court documents.
The online forum had a private section that was only available to members who shared imagery of children they had abused themselves.
Several police investigations in recent years have broken up other enormous dark web forums, including one known as Child’s Play that was reported to have had over a million user accounts.
No details have emerged on the investigation in Florida that led to Tuesday’s shooting. Hours after the gunfire, there was still a heavy police presence around the apartment complex.
George L. Piro, the special agent in charge of the F.B.I.’s Miami field office, said agents “meticulously plan” and execute search warrants almost daily.
“The vast majority of these warrants occur without incident,” he said. “The operations this morning in Sunrise ended tragically, with the subject opening fire on the members of the search team.”
Throughout the day, the police maintained a perimeter about half a mile north, restricting access to the complex and surrounding areas. Officers cordoned off a large swath of Nob Hill Road and set up a staging site in a nearby rehabilitation hospital.
The agents killed on Tuesday were the first who had been fatally shot in the line of duty since November 2008, when Special Agent Samuel S. Hicks, 33, was killed while serving a search warrant, according to the F.B.I.
Mr. Hicks was part of a team of agents executing an arrest warrant at a house near Pittsburgh that was connected to a drug trafficking ring, the bureau said.
The shooting on Tuesday was one of the worst in the history of the F.B.I.
In 1986, two agents were killed in Miami and five others wounded during the pursuit of two violent bank robbers who were also killed in the exchange. The gun battle at the Suniland Shopping Plaza in what is now the village of Pinecrest was the costliest in F.B.I. history.
In November 1994, two agents were killed, a third agent was wounded and a 15-year-old boy was shot in the leg when a man came into the cold case squad room of Police Headquarters in Washington and opened fire with an assault rifle, according to the F.B.I.
A police detective was also killed during the shooting. The gunman, a suspect in a triple killing a month earlier, had left notes saying he planned to kill members of the local police homicide unit, the F.B.I. said.
On Tuesday, police officers stood in a somber line saluting as a gurney carrying one of the bodies draped in an American flag was placed into a fire rescue truck at the Broward Health Medical Center in Fort Lauderdale. A procession of dark law enforcement S.U.V.s and motorcycles with sirens and lights then escorted the ambulance to the county medical examiner’s office.
Patricia Mazzei and Johnny Diaz reported from Miami, Adam Goldman from Washington, and Christina Morales from Coral Springs, Fla., Weston, Fla., and Miramar, Fla. Katie Benner and Seamus Hughes contributed reporting from Washington, Maria Cramer from Maplewood, N.J., Gabriel J.X. Dance, Nicholas Bogel-Burroughs and Michael H. Keller from New York, and Michael Majchrowicz from Sunrise, Fla., and Pembroke Pines, Fla. Susan C. Beachy contributed research.