The Justice Department has arrested Florida resident Joshua Ryne Goldberg for allegedly distributing documents on manufacturing explosives as part of a bomb plot for a 9/11 memorial event in Kansas City, Missouri.

US Attorney Lee Bentley announced the arrest on Thursday. Goldberg, 20, was charged with alleged “illegal distribution of information relating to explosives, destructive devices, and weapons of mass destruction.” The distribution of such material is considered a federal crime.

According to the criminal complaint, FBI Special Agent William Berry was conducting an investigation into the attack on the May 2015 Mohammed Art Exhibit and Contest in Garland, Texas, when he tracked down a Twitter account called “Australi Witness,” which was posting tweets calling for an attack on the exhibition.

The Twitter user posted maps of the center and called for people to attack “with your weapons, bombs, or knives.” Berry also found a statement by Australi Witness that implied he was in Australia and working with contacts in the US to carry out attacks.

The FBI said in the complaint that Goldberg also used the name “AusWitness” and was in daily contact with an FBI informant, or confidential human source (CHS), through direct messages from July of 2015.

AusWitness sent the CHS five links to websites on how to manufacture a bomb during their exchange, according to the FBI. During their discussions, the CHS proposed targeting the upcoming memorial in Kansas City, Missouri, which will commemorate the terrorist attacks of September 11, 2001, the complaint said. The event is to be attended by the general public and firefighters.

The complaint went on to say that AusWitness instructed the CHS to make a pressure cooker bomb and fill it with nails, metal, and other items dipped in rat poison. He also allegedly instructed the CHS to plant the bomb at the memorial event close to the crowd and to make sure it was well hidden.

Berry said Goldberg’s identity was tracked down by the IP address associated with AusWitness and another identity Goldberg revealed as “AusSecret,” which was tracked to Goldberg’s family home in Florida.

Information from the Australian Federal Police revealed that an informant identified as LM had told them that Australi Witness was Joshua Goldberg, an “online troll” and “proponent of radical free speech,” who was responsible for “hoax events” on the internet.

The FBI conducted surveillance on Goldberg’s family home and arrested him on September 9.

In the complaint, the FBI said Goldberg allegedly waived his rights and spoke to law enforcement, admitting he was behind AusSecret, AusWitness and Australi Witness, and that he had sent out the message calling for an attack on the Mohammed Art Exhibition and Contest.

He allegedly also admitted that he sent bomb manufacturing instruction links to the CHS, claiming “that he intended for the individual (CHS) to either kill himself creating the bomb or, if not, that he intended to alert law enforcement just prior to the individual detonating the bomb, resulting in Joshua Goldberg to receive credit for stopping the attack,” the complaint said.

If convicted, Goldberg faces a maximum penalty of 20 years in federal prison.The FBI and Department of Homeland Security carried out several arrests earlier this year connected to heightened terror threats surrounding the July 4 celebrations. The agency’s director, James Comey, said the FBI has arrested more than 10 people, which he believes stopped acts of violence in the month before the holiday.