The U.S. Department of Justice announced that the FBI detained an 18-year-old in Idaho this past weekend after learning of his “violent plot” and “truly horrific” plan to attack churches in Coeur d’Alene on behalf of the terrorist group ISIS.

Following the FBI’s claim that Alexander Mercurio planned to “incapacitate his father, restrain him using handcuffs, and steal his firearms to use for maximum casualties” in an attack he had been planning to carry out in the northern Idaho resort city on Sunday, April 7, he is now facing a federal charge of attempting to provide material support or resources to a designated foreign terrorist organization.

In a criminal complaint, the FBI says the investigation began when Mercurio, who is a resident of Coeur d’Alene, “reached out to confidential human sources online and indicated his support for ISIS and terrorist organizations, more generally.”

“Mercurio spread ISIS propaganda online and solicited ISIS’s involvement in and approval of his propaganda efforts, discussed traveling from the United States to join ISIS, [and] considered and planned ways to support ISIS financially,” an FBI investigator wrote in the complaint.

“His attack plan involved using flame-covered weapons, explosives, knives, a machete, a pipe, and ultimately firearms,” the investigator added. “His plan grew more precise as he eventually identified the specific church and date on which he planned to attack.”

The FBI investigator also said Mercurio “made a ba’yah statement, pledging his allegiance to ISIS and stating his intention to die while killing others on behalf of ISIS.”

Fox News reported: “But on Saturday afternoon, FBI agents carried out a search warrant at Mercurio’s house and took him into custody while allegedly finding items linked to the plot, including a ‘metal pipe,’ ‘a black Smith and Wesson fixed blade knife’ and a ‘machete,’ according to the complaint. Mercurio now faces up to 20 years in federal prison if convicted on the federal charge.”

The FBI’s Joint Terrorism Task Force (JTTF) has arrested Mercurio for planning a violent attack. He is currently in custody and awaiting his initial court appearance.

Attorney General Merrick B. Garland said in a statement: “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. 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. The Justice Department will continue to relentlessly pursue, disrupt, and hold accountable those who would commit acts of terrorism against the people and interests of the United States.”

FBI Director Christopher Wray said: “The defendant allegedly pledged loyalty to ISIS and sought to attack people attending churches in Idaho, a truly horrific plan which was detected and thwarted by the FBI’s Joint Terrorism Task Force. This investigation demonstrates the FBI’s steadfast commitment to work with our law enforcement partners to stop those who wish to commit acts of violence on behalf of – or inspired by – foreign terrorist groups.”

“Across the Department of Justice, and in my office, we have no higher calling than to protect our nation and our communities from terrorism. Along with our law enforcement partners, my office will always remain laser-focused on this part of our mission,” said U.S. Attorney Josh Hurwit for the District of Idaho.

“I want to thank the FBI for its tireless work on this investigation and its thorough efforts to prevent violence. The support from local law enforcement was also integral to successfully disrupting the alleged plot,” Hurwit added.

“This case should be an eye-opener to the dangers of self-radicalization, which is a real threat to our communities. Protecting the American people from terrorism remains the FBI’s number one priority, and we continue to encourage the public to report anything suspicious to the FBI or your local law enforcement,” said Special Agent in Charge Shohini Sinha of the Salt Lake City FBI.