A Muslim convert is in custody after authorities say he planned to set off hand grenades in a crowded Illinois shopping mall on Dec. 22 as part of a plan to wage 'violent jihad' against U.S. citizens.

After being tipped by an acquaintance of Derrick Shareef, 22, the FBI says it taped him discussing his plan to put hand grenades into garbage cans, causing clouds of shrapnel to blast shoppers in a crowded mall the Friday before Christmas. "This is a warning to those who disbelieve," he allegedly said.

Federal agents say Shareef tried to make an unusual trade: two stereo speakers for a 9 mm pistol and the grenades he would need to pull off his alleged plot.

Authorities waited to arrest the man until Wednesday, when they say he tried to make the trade with an undercover agent in a Rockford parking lot.

"The Joint Terrorism Task Force was all over this … and the only person involved in this plot was Mr. Shareef and two people working for the government," U.S. Attorney Patrick J. Fitzgerald said during a press conference from Chicago Friday afternoon.

Shareef was charged Friday with crimes that could send him to prison for the rest of his life.

"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.

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

The acquaintance went straight to the FBI, officials said.

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 he was allegedly eyeing included government facilities such as courthouses and City Hall, authorities said.

The 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 various 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.

A spiritual leader of Rockford-area Muslims commended authorities for intercepting the alleged plot and reiterated "the Muslim community's condemnation of terrorism in the name of Islam," said Shpendim Nadzaku, imam of the Muslim Association of Greater Rockford.

Asked if he had ever met Shareef, Nadzaku said: "No one in the community has any clue as to who this person is — he's completely anonymous."

The door of a Genoa town home that is the last known address for Shareef went unanswered Friday, although a female inside was seen turning off a light as a reporter stood outside.

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. The latter charge carries a maximum sentence of life in prison.

Defense attorney Michael B. Mann declined comment.

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 the affidavit.

Authorities say that on Wednesday, Shareef met an undercover agent working for the FBI-led Joint Terrorism Task Force who showed him four non-working grenades and a pistol with non-working bullets. Shareef was arrested when he allegedly offered the speakers in exchange.

The Associated Press contributed to this report.