A dealer in historic Mormon documents was critically injured today when a bomb went off in his car -- the third such explosion here in two days.

Mark Hofmann, 31, who underwent surgery at LDS Hospital after the blast, was found to have "incriminating" evidence in the car linking him to the earlier bombings, in which two people died, Police Chief Bud Willoughby said tonight.

Federal charges will be filed against Hofmann in the fatal bombings, authorities said.

There may have been three other people targeted for bombings and it is possible that others were involved in the plot, said Jerry Miller of the federal Bureau of Alcohol, Tobacco and Firearms. Authorities were studying revenge as a motive, he added.

"Tomorrow morning we will present information to the U.S. attorney charging Mark Hofmann with violation of federal firearm laws and explosives laws," Miller said.

Hofmann had helped acquire a controversial document involving the founding of the Church of Jesus Christ of Latter-day Saints. The two people killed in Tuesday's blasts also were linked to the 19th-century document, known as the "white salamander" letter, which runs counter to official Mormon accounts of how the religion started.

The first victim, Steven F. Christensen, 31, died Tuesday morning in an explosion at his downtown office. Two years ago, Christensen bought the salamander letter from Hoffman. The letter's references to magic practices by Joseph Smith, the founder of the Mormon church, angered many church members. The white salamander was a common symbol used in magical practices of the era.

The second victim was Kathleen Sheets, 50, wife of Christensen's former business associate, J. Gary Sheets. Historical researcher Brent Metcalfe said J. Gary Sheets helped finance a $20,000 study to determine the authenticity of the letter, which Christensen donated to the church last spring.

A man matching Hofmann's description was seen carrying a package for Christensen prior to the first bombing Tuesday, Salt Lake County Sheriff Pete Hayward said today. Detectives armed with search warrants had been looking for Hofmann.

Police Chief Willoughby said a witness to today's bombing "saw Hofmann carrying either a box or a briefcase when he opened the car," which was parked about a block from the Mormon Temple.

Police said the bomb that injured Hofmann appeared similar to those found on Tuesday -- sections of pipe filled with explosives. Christensen and Kathleen Sheets were killed by bombs concealed in cardboard boxes, the first bearing Christensen's name and the second Gary Sheets'.

Police had said Tuesday that the bombs might have been planted by a disgruntled investor in the financially troubled CFS Financial Corp., of which Sheets was former president and Christensen was a former director. Investigators also were considering a possible link to the Mormon church when the third explosion occurred.

Hofmann began collecting church memorabilia when he was 12, according to a 1982 interview in The Sunstone Review, an independent journal for Mormon intellectuals.

"Although I do have fun," he said in the interview, "it's really not as romantic as it sounds. It seems like you always have people who hate you or are mad at you."

The salamander letter was written in 1830 by Martin Harris, a close associate of Smith.