Updated

An alleged wannabe terrorist who reportedly plotted a church shooting in support of ISIS is due in a Michigan court Monday on marijuana and gun charges.

Khalil Abu-Rayyan, 21, has yet to be charged with terrorism-related crimes, but he’s been investigated for a terror connection since May. U.S. attorney’s office spokeswoman Gina Balaya said Abu-Rayyan would have a court-appointed attorney at his Monday hearing. She said Abu-Rayyan has been under constant surveillance due to the possibility he could try to attack a church, police officers or others.

He was likely acting alone, authorities said.

In a criminal complaint, the FBI said Abu-Rayyan expressed support for ISIS "propaganda" postings on social media, including videos of its members beheading captives. It also said he made several incriminating statements to an undercover agent, including that he supported ISIS, had a "desire to commit a martyrdom operation," and that he wanted to behead someone.

According to the complaint, Abu-Rayyan told the undercover officer he planned to "shoot up" a Detroit church but that his father found the gun, bullets and mask he was going to use. He also said he bought a "cowboy gun," but he decided not to go through with the attack because it only held six bullets and he'd have to keep reloading it, it says.

Abu-Rayyan pleaded guilty last month to a pot possession charge, and he faces a Feb. 16 trial for a concealed weapon charge. Both stem from an October arrest.

The Associated Press contributed to this report.