Alexander Scott Mercurio, 18, was charged with attempting to provide material support or resources to a designated foreign terrorist organization, according to a Justice Department news release. The FBI's Joint Terrorism Task Force conducted the investigation.
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Mercurio planned to attack churches in Coeur d'Alene, Idaho, on Sunday "using weapons, including knives, firearms, and fire," according to court documents cited by the Justice Department.
Investigators believe Mercurio's alleged efforts to carry out an attack intensified following the March attack that killed 144 people at a concert hall complex near Moscow, according to a US law enforcement official. Russian and US authorities have blamed an ISIS group for that attack.
"As alleged in the complaint, the defendant swore an oath of loyalty to ISIS and planned to wage an attack in its name on churches in Coeur d'Alene, Idaho," Attorney General Merrick Garland said in the release.
"Thanks to the investigative efforts of the FBI, the defendant was taken into custody before he could act, and he is now charged with attempting to support ISIS's mission of terror and violence," he added.
CNN could not immediately identify an attorney for Mercurio.
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According to court documents, Mercurio had online and in-person meetings with a confidential source working with the FBI and "proceeded to express his support for terrorist organizations, specifically ISIS."
He planned to attack a church on April 7, 2024, which he selected so that it would occur before the conclusion of Ramadan, FBI Task Force officer John Taylor said in an affidavit.
Mercurio, according to court documents, allegedly brought butane canisters, a metal pipe, and also planned to "harm his father and acquire firearms" to use in the attack. Days before the planned attack, he recorded a statement pledging his allegiance to ISIS.
In the video, Mercurio is seen holding a knife in front of an ISIS flag, court documents said.
During a search of his parents' home, police found "items consistent with his planned attack," court documents stated. Some of the items found in a toolbox included a "metal pipe, handcuffs, folding saw, head coverings, two cannisters of butane fuel, and machete." Multiple rifles and handguns were also discovered in his father's bedroom.
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Mercurio "stated he intended to incapacitate his father with a pipe, handcuff him, and use the firearms locked in the closet to attack the church," court documents say.
He faces a maximum penalty of 20 years in federal prison if convicted, according to the Justice Department. He is currently in custody awaiting his initial court appearance.
"This case should be an eye-opener to the dangers of self-radicalization, which is a real threat to our communities," said Special Agent in Charge Shohini Sinha of the Salt Lake City FBI.
CNN's Rashard Rose, Melissa Alonso, Evan Perez and Hannah Rabinowitz contributed to this report.
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