Investigators said Derrick Shareef, 22, an American citizen from Rockford, was acting alone and never actually obtained any grenades. He was arrested Wednesday when he met with an undercover agent in a parking lot to trade a set of stereo speakers for four hand grenades and a gun, authorities said.

"He fixed on a day of December 22nd on Friday ... because it was the Friday before Christmas and thought that would be the highest concentration of shoppers that he could kill and injure," said Robert Grant, the agent in charge of the Chicago FBI office.

Authorities said Shareef had been under investigation since September, when he told an acquaintance that "he wanted to commit acts of violent jihad against targets in the United States as well as commit other crimes."

The acquaintance immediately informed the FBI, officials said.

Federal officials said Shareef planned to set off four hand grenades in garbage cans at the CherryVale shopping mall in Rockford, about 90 miles northwest of Chicago.

Other potential targets that Shareef allegedly discussed included government facilities such as courthouses and city hall, authorities said.

An affidavit quoted him as saying: "I just want to smoke a judge."

Shareef was born in the United States and converted to Islam, officials said. They believe he might have learned about jihad through videos and Web sites.

"While these are very serious charges, at no time was the public in any imminent peril," U.S. Attorney Patrick J. Fitzgerald said in a statement.

Shareef appeared briefly before a judge Friday and was ordered held without bond. He was charged with one count of attempting to damage or destroy a building by fire or explosion and one count of attempting to use a weapon of mass destruction.

Defense attorney Michael B. Mann declined to comment on the charges.

Shareef and his acquaintance cased the mall on Nov. 30, discussing the layout and spots where they might set off several grenades simultaneously to create more pandemonium, according to an FBI affidavit.

A spokeswoman for the mall said officials were cooperating with the investigation but referred all other questions to the U.S. attorney's office.