A man has been charged with plotting to set off an explosion at a 9/11 event in Missouri.
Joshua Ryne Goldberg, 20, was arrested by the FBI Joint Terrorism Task Force at his parents' home near Jacksonville, Florida on Thursday.
According to a criminal complaint, he started communicating with an informant online in July.
He allegedly instructed the informant on how to make a bomb he wanted to detonate at a 9/11 memorial event in Kansas City.
"What weapons do you have brother?" he wrote in one message, cited in the criminal complaint. "I can send you guides on how to make bombs if you need help making them."
He allegedly encouraged the informant to build a pressure cooker bomb like those set off at the Boston Marathon bombing.
He allegedly wrote: "Put as much sharp stuff as you can in there" and "use shards of metal and nails."
The bomb was never built.
Prosecutors say Goldberg thought he was speaking with someone who wanted to help his cause - but the person was actually an FBI informant who shared the conversations with authorities.
While speaking online, Goldberg presented himself as a Muslim living in Australia who supported ISIS, according to court documents. But the computer was tracked down to Florida.
Australian police said they interviewed a witness who said Goldberg's online personas were part of a hoax and that he was actually a "proponent of radical free speech," The Associated Press reported.
Police arrested him on Thursday and if convicted, he could get 20 years in prison. A judge set a Tuesday bail hearing for Goldberg.
In recent days, there have also been reports that Al Qaeda is targeting some of the wealthiest people in America for assassination.
The Al Qaeda online magazine Inspire has named U.S. billionaires like Microsoft founder Bill Gates, financier Warren Buffet and Michael Bloomberg.
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