Federal authorities arrested a man they say collaborated with the bomber of a fertility clinic in May, alleging he supplied chemicals used to make explosives and traveled to California to experiment with them in the bomber’s garage months before the attack.

The two men had connected in fringe online forums over their shared beliefs against human procreation, authorities told reporters Wednesday. The blast gutted the fertility clinic in Palm Springs and shattered the windows of nearby buildings, with officials calling the attack terrorism.

Guy Edward Bartkus, the bomber from California, died in the May 17 explosion. Authorities arrested his alleged collaborator, Daniel Park of Washington, on Tuesday after he was extradited from Poland, where he’d fled four days after the attack.

Park spent years stocking up on ammonium nitrate, a chemical that can be used to make explosives, before shipping it to Bartkus and later visiting him in Twentynine Palms, California. He stayed for about two weeks and the two conducted bomb-making experiments in Bartkus’ room and a detached garage, said Akil Davis, the FBI’s assistant director in charge.

Park, 32, was taken into custody on Tuesday night at New York’s John F. Kennedy Airport, U.S. Attorney Bill Essayli told reporters. Park is expected to make his first court appearance Wednesday in Brooklyn.

Authorities searched Park’s home in Kent, a suburb of Seattle, and found “an explosive recipe that was similar to the Oklahoma City bombing,” Davis said.

Park shipped 180 pounds of ammonium nitrate in January to Bartkus and bought another 90 pounds of the chemical and had it shipped to Bartkus days before the March 17 explosion, authorities said. Park purchased ammonium nitrate online in several purchases between October 2022 and May 2025, according to the complaint.

Park and Bartkus, age 25, had met in online forums dedicated to the anti-natalist movement, bonding over a “shared belief that people shouldn’t exist,” Davis said.

Anti-natalism is a fringe theory that opposes childbirth and population growth and believes people should not continue to procreate. Officials said Bartkus intentionally targeted the American Reproductive Centers, a clinic that provides services to help people get pregnant, including in vitro fertilization and fertility evaluations.

However, investigators haven’t said if Bartkus intended to kill himself in the attack or why he chose the specific facility. He tried to livestream the explosion but failed, the FBI says.

Park appeared to be a frequent poster in an anti-natalist Reddit forum going back nearly a decade, according to court papers. In 2016, he spoke of recruiting others to the movement, which he described as hopeful. “When people are lost and distraught, death is always an option,” he allegedly wrote.

More recently, this past March, Park posted in the group that he was seeking to find fellow anti-natalists in and around Washington to “start some protests or just any in-person events,” according to court papers. The post did not receive any public comments.

Scott Sweetow, a retired ATF explosives expert, had previously said the amount of damage caused indicated that the suspect used a “high explosive” similar to dynamite and TNT rather than a “low explosive” like gun powder.

Those types of explosives are normally difficult for civilians to access, but increasingly people are finding ways to concoct explosives at home, he said.

“Once you know the chemistry involved, it’s pretty easy to get stuff,” Sweetow said. “The ingredients you could get at a grocery store.”

Davis previously called the explosion possibly the “largest bombing scene that we’ve had in Southern California.”

(AP)