NEWARK, N.J. (AP) – A Wisconsin grocery store clerk surrendered Friday on charges in an Internet hoax threatening a “dirty bomb” plot against U.S. football stadiums and told prosecutors he had posted the same message about 40 times over the past few weeks, federal authorities said.

Jake J. Brahm, of Wauwatosa, Wis., surrendered to the U.S. Marshal’s Service on Friday morning and was scheduled to appear in court in Milwaukee later in the day.

He was charged in a sealed criminal complaint filed Thursday in Newark, U.S. Attorney Christopher Christie said.

One of the seven stadiums allegedly targeted was Giants Stadium in East Rutherford, N.J.

Christie said Brahm admitted that between September and Wednesday he had posted the same threat about 40 times on various Web sites. Authorities would not discuss how or when they became aware of the postings.

“These types of hoaxes scare innocent people, cost business resources and waste valuable homeland security resources. We cannot tolerate this Internet version of yelling fire in a crowded theater in the post-9/11 era,” Christie said.

Brahm was first taken into custody by police in Wauwatosa on Wednesday based on information authorities received that he was the source of the Internet threat, federal authorities said. FBI agents interviewed him that night, and the FBI said Thursday it had determined the threat was a hoax.

A joint statement from the FBI and Homeland Security Department said fans “should be reassured of their security as they continue to attend sporting events this weekend.”

An FBI official in Washington, who spoke on condition of anonymity because the case is still under investigation, told The Associated Press that the man acknowledged posting the phony stadium threat as part of a “writing duel” with a man from the Brownsville, Texas, area to see who could post the scariest threat.

The Texas man corroborated the story, the official said. The threat, dated Oct. 12, appeared on the Web site “The Friend Society,” which links to various online forums and off-color cartoons.

Its author, identified in the message as “javness,” said trucks would deliver radiological bombs Sunday to stadiums in Miami, Atlanta, Seattle, Houston, Cleveland, Oakland, Calif., and the New York City area, and that Osama bin Laden would claim responsibility.

The agency alerted authorities Wednesday in the cities mentioned, as well as the NFL and the National Collegiate Athletic Association. But the FBI and Homeland Security said there was no intelligence indicating such an attack might be imminent.

NFL spokesman Greg Aiello said stadiums are well protected through “comprehensive security procedures” that include bag searches and pat-downs.

Relatives of Brahm declined to comment Friday.

Brahm’s attorney, Patrick Knight, said he has not seen anything to indicates Brahm meant any real harm.

“I think once it got out there, obviously you lose all control of the manner and the context in which the posting occurred,” Knight said.

Brahm worked as a grocery clerk at Outpost Natural Foods, a co-op near his house, said Jeremy Layman, assistant store manager. He said Brahm made his shifts on time and was not a concern.

“He was a normal guy. That’s all we’re going to say at this time,” Layman said.

Erik Vasys, spokesman with the FBI in San Antonio, said there would be no charges against the Texas man.

“I was advised he interacted with this gentleman in Milwaukee, just downloaded some things, but he was not part of the hoax writing,” Vasys said.

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