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The FBI has arrested a 19-year-old North Carolina man for allegedly plotting an ISIS-inspired terrorist attack — after being tipped off to his disturbing behavior by his father.

Justin Nojan Sullivan's parents were in court on Monday for his appearance and told reporters outside that they were shocked by the allegations in a criminal complaint.

That court document says that in addition to planning an attack that would wipe out hundreds of people, Sullivan allegedly also wanted someone to kill his parents.

The young man was arrested Friday after the FBI found a silencer in the Morganton house where he lived with his father and stepmother.

Sullivan had asked another man to build a silencer for him — and that person turned out be an undercover FBI operative, who built the silencer for him, according to court papers.

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It's unclear how much of a threat Sullivan actually posed.

He certainly talked big, telling the undercover he might want to kill as many as 1,000 people, set off a big vehicle bomb or use chemical weapons, a criminal complaint says. He even talked about coating bullets with cyanide and robbing banks, the feds say.

But he apparently wasn't on investigators' radar until April, when his father called 911 to report that he was destroying Buddha figurines and had doused their religious objects with gasoline.

"We are scared to leave the house," the father told the operator, according to the court documents.

Sullivan could he heard in the background asking, "Why are you trying to say I'm a terrorist?"

Related: Inside the Mind of American ISIS Wannabes

Weeks later, an undercover operative made contact with Sullivan, who allegedly told him, "I liked IS from the beginning, then I started thinking about death and stuff so I became a Muslim."

The FBI says Sullivan talked about buying an assault rifle from a gun show in North Carolina and shoot people last weekend "because his parents would be out of town at the time."

He did not buy a rifle before he was arrested Friday but allegedly planned to purchase one at the Hickory Gun Show last weekend.

The criminal complaint says Sullivan confessed to plotting an attack, telling authorities that he looked for possible targets in the online Yellow Pages and had asked the undercover agent to kill his parents.