A Florida man is charged with plotting to set off an explosion at a 9/11 event. The FBI Joint Terrorism Task Force arrested 20-year-old Joshua Ryne Goldberg Thursday in Florida. Prosecutors say he told an online informant how to make the bomb he wanted.

Investigators originally thought the suspect was recruiting people to carry out attacks from a location in Australia, reports CBS News correspondent Jeff Pegues.

It turns out Goldberg was in the U.S., in a home near Jacksonville, where he was taken into custody. He shares the home in Orange Park with his parents.

CBS affiliate KCTV reports that the arrest took Goldberg's family by surprise.

"We have no information. There hasn't been any kind of pre-hearing or anything. They came and took Joshua today. That's all I can tell you," said his father, Frank Goldberg to KCTV.

Neighbors said Goldberg stood emotionless and shirtless on the front porch when officers arrested him.

"He was a lost soul willing to engage in terrorist activities to fulfill his needs of feeling important," said retired FBI agent Michael Tabman after reviewing the 34-page complaint.

KCTV reports that the criminal complaint says that Goldberg intended for the individual to either kill himself creating the bomb or, if not, Goldberg intended to alert law enforcement just prior to the individual detonating the bomb. Then Goldberg would be credited with stopping the attack.

According to court documents, he had set his sights on bombing a 9/11 memorial event -- the Kansas City Stair Climb.

Firefighters participating in the stair climb in Kansas City. CBS affiliate KCTV

On the event website, the Kansas City 9-11 Memorial Stair Climb is described as an event where 343 firefighters embark on a 110 story climb to the top of the Town Pavilion high rise in downtown Kansas City. The event is held in remembrance of the 343 firefighters killed on Sept. 11, 2001.

There are other similar events across the country.

Investigators said he was communicating online with someone he thought was sympathetic to his cause but who was actually an FBI informant, and the online conversations were being monitored. According to investigators, Goldberg encouraged the informant to build a pressure cooker bomb similar to what was used in the Boston Marathon bombing.

Orange Park man allegedly planned the attack for an event in Kansas City. CBS affiliate JAX

He allegedly wrote, "Put as much sharp stuff as you can in there" and "use shards of metal and nails."

It was enough for police to make the arrest.

If convicted, Goldberg could get up to 20 years behind bars.

According to court documents, online, Goldberg presented himself as a Muslim living in Australia who supported ISIS. But ultimately, a bomb was never built and Goldberg was doing his planning using his mother's computer at the family home.