A Philadelphia man pleaded guilty to falsely claiming that a man he disagreed with in a fantasy football league chat was planning a mass shooting in Norway, a hoax that Norwegian and U.S. authorities spent hundreds of hours investigating, federal prosecutors said Wednesday.

The case against Matthew Gabriel, 25, is the tip of the iceberg of a larger problem: Each year authorities in the U.S. alone receive thousands of calls and online messages from people falsely claiming they are going to shoot up schools, detonate bombs, or kill random people.

Prosecutors say a smaller segment of those making phony claims include people like Gabriel, who attempt to frame others by making authorities believe an attack is about to happen.

Gabriel sent an anonymous tip in August of last year to the Norwegian Police Security Service, falsely claiming that man was headed to Oslo with deadly intentions, prosecutors said.

"He has a shooting planned with multiple people on his side involved," Gabriel said in the tip, according to federal court documents. "They plan to take as many as they can at a concert and then head to a department store. I don’t know any more people then that, I just can’t have random people dying on my conscience."

But in fact, the man traveling abroad was harmless and was not planning anything sinister, court papers said.

Gabriel made the false claim because he "had an online disagreement with a member of his fantasy football chat group," the documents said. He contacted Norwegian authorities because he had learned that the football chat member was going to study abroad in Norway.

Gabriel could face up to five years in prison. He's expected to be sentenced in January, according to court records.

Second threat made to college campus after FBI visit

Federal prosecutors said Gabriel's first false threat was sent to Norwegian authorities, naming the person he disagreed with in a fantasy football group. He chose Norway after learning the fantasy league member was studying abroad in August 2023.

Police in Norway and the U.S. spent five days investigating the threat. Gabriel admitted during an FBI interview he submitted and falsified the tip, according to prosecutors.

Then, on March 22 of this year, Gabriel sent an email posing as another person to the University of Iowa with the subject line “Possible Threat.” The email, documented in court records, said:

Hello, I saw this in a group chat I’m in and just want to make sure everyone is safe and fine. I don’t want anything bad to happen to any body. Thank you. A man named [PERSON 1] from I believe Nebraska sent this, and I want to make sure that it is a joke and no one will get hurt.

Jacqueline C. Romero, the United States Attorney for the Eastern District of Pennsylvania, said in a statement: "While already being prosecuted for one hoax threat spurred by, of all things, his fantasy football league, Matthew Gabriel inexplicably decided to send another.”

Nation overwhelmed with false violent threats

Romero advised "keyboard warriors" to think before posting online about violent threats. She said Gabriel's threats caused extreme disruption and pulled authorities away from actual investigations.

"Hoax threats aren’t a joke or protected speech, they’re a crime," she said. "My advice to keyboard warriors who’d like to avoid federal charges: always think of the potential consequences before you hit ‘post’ or ‘send.’”

That extreme disruption is seen in Springfield, Ohio with numerous bomb and shooting threats called into schools, colleges and city hall. The threats started after former President Donald Trump and his running mate Ohio Sen. JD Vance spread debunked claims about Haitian immigrants eating pets.

Springfield residents and Haitians pleaded with Trump, Vance and others to stop making the false claims. Ohio Gov. Mike DeWine, a Republican, called the rumors "a piece of garbage" on Sunday.

"These are positive influences on our community in Springfield and any comment about that otherwise I think is hurtful and is not helpful to the city of Springfield and the people of Springfield," he said.

In Florida, a sheriff resorted to posting mug shots and doing "perp walks" of students who created mass shooting hoaxes. Volusia County Sheriff Mike Chitwood made the announcement after authorities received more than 54 school threat tips through Fortify Florida, an app used to securely report suspicious activity.

Police in Missouri, Nebraska, New Jersey, Pennsylvania and Texas all reported having to investigate hoaxes and charge students for making them. They came a week after a shooting at Apalachee High School in Georgia left four people dead.

Nick Suplina, senior vice president for law and policy of Everytown for Gun Safety, previously told USA TODAY the best way to assess the legitimacy of a school shooting threat is if a person has access to guns. He added it's "just bluster" if a person doesn't have access.

Contact reporter Krystal Nurse at [email protected]. Follow her on X, formerly Twitter,@KrystalRNurse.