LOS ANGELES >> Federal authorities arrested a man they say collaborated with the bomber of a fertility clinic in May, alleging that 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 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 and possibly the largest bomb scene in Southern California. The clinic was closed, and no embryos were damaged.

Guy Edward Bartkus of California, the bomber, died in the May 17 explosion. Authorities arrested Daniel Park, 32, of Washington state Tuesday after he was extradited from Poland, where he fled to four days after the attack. Park is charged with providing and attempting to provide material support to terrorists.

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. He stayed for about two weeks earlier this year, and the two conducted bomb-making experiments in the detached garage of Bartkus’ family home, said Akil Davis, the FBI’s assistant director in charge.

Park, 32, was taken into custody at New York’s John F. Kennedy Airport, U.S. Attorney Bill Essayli told reporters. He appeared in federal court Wednesday in Brooklyn and, through his lawyer, waived his right to a detention hearing in New York.

Judge Cheryl Pollak ordered him to remain detained, saying he posed a serious risk. He will be sent to California, and federal defender Jeffrey Dahlberg said Park reserves the right to have a hearing on probable cause there. A date for that hearing has not been set, prosecutors said.

A cache of chemicals

Authorities searched Park’s home in Kent, a suburb of Seattle, and found large quantities of several chemicals and handwritten notes of chemical explosive equations, according to a federal complaint. One was for “an explosive recipe that was similar to the Oklahoma City bombing,” Davis said, a reference to the 1995 explosion that killed 168 people and was the deadliest homegrown attack in U.S. history.

Park shipped 180 pounds of ammonium nitrate to Bartkus in January and bought 90 pounds and had it shipped to him days before the explosion, authorities said. Park purchased ammonium nitrate online in several transactions between October 2022 and last month, according to a federal complaint.

Three days before Park visited him in January, Bartkus asked an AI chat application about explosives, detonation velocity, diesel and gasoline mixtures, the complaint said. The discussion centered on how to create the most powerful blast.

In a search of Bartkus’ family’s home, authorities found “large quantities” of explosives material. Bartkus’ relatives told investigators the two were “running experiments” in the garage. Bartkus’ family did not raise any concerns to officials, authorities said.

An analysis of the blast site showed that ammonium nitrate could have been used in the explosive mixture.