COEUR d’ALENE — The 18-year-old Coeur d’Alene resident accused of planning to attack local churches on behalf of the terrorist organization ISIS pleaded not guilty to a criminal charge in federal court Wednesday morning.

Alexander S. Mercurio is charged with attempting to provide material support to a designated foreign terror organization. Prosecutors say Mercurio told confidential sources he planned to donate “every last cent” in his bank account to ISIS, a sum of about $11,000, before carrying out a “martyrdom operation” in Coeur d’Alene on April 7.

U.S. marshals uncuffed Mercurio’s hands as he entered the courtroom at the federal courthouse in Coeur d’Alene. He wore a red and white striped jumpsuit.

If convicted, Mercurio faces a maximum penalty of 20 years in prison and up to a lifetime of supervised release.

All assets belonging to Mercurio are subject to forfeiture to the United States upon conviction, as well as any property “which constitutes or is derived from proceeds traceable to the offense or a conspiracy to commit such offense.” In court Wednesday, Mercurio denied the forfeiture allegation.

A multi-year investigation by the FBI’s Joint Terrorism Task Force culminated in Mercurio’s arrest April 6, the day before federal prosecutors believe he planned a deadly attack on churchgoers in Coeur d’Alene.

“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,” FBI Director Chris Wray said in a news release Monday.

Mercurio allegedly planned to incapacitate churchgoers by beating them with a metal pipe, “slit their throats with a knife or a machete” and then start fires inside the building.

Mercurio reportedly told a confidential source that he considered beating and tying up his father before commencing an initial church attack, so as to spare his father’s life but prevent him from alerting police. He also planned to use his father’s car for transportation and wanted to steal his father’s guns, according to a criminal complaint.

In the weeks leading up to his arrest, Mercurio indicated he was determined to attack “various churches” in Coeur d’Alene during Ramadan, according to court records. Muslims throughout the world observe Ramadan as a month of fasting, prayer, reflection and community. Mercurio also reportedly expressed frustration that he had not taken action yet.

“I don’t have the desire to do anything except jihad,” he reportedly wrote March 22. “A craving for mayhem and terror.”

He described plans to build a “crude flamethrower” or a “flame sword,” according to court records, and purchased a metal pipe. A search of his bedroom reportedly yielded the pipe, as well as a machete, a black Smith and Wesson fixed blade knife, a folding saw, handcuffs, two canisters of butane fuel, two lighters and a black and white “ISIS” flag, as well as other materials.

Mercurio waived his right to a detention hearing Wednesday. That means he will remain in custody at the Kootenai County jail while a trial is pending. Proceedings will remain in Coeur d’Alene.

A jury trial in the case is scheduled to begin May 28, with U.S. District Chief Judge David Nye presiding.