The Unseen Cavaliers car club met Wednesday nights in the parking lot of an unremarkable strip mall 25 miles south of Washington, opening its gatherings to anyone who claimed an interest in that particular model Chevrolet. But as daylight faded last Wednesday, there were no engines idling and no car stereos thumping.

The club's leader, Patrick S. Walsh, 20, is in jail, accused of engineering Maryland's most extensive residential arson in recent memory -- fires that raged through an upscale development in Charles County that was attracting mostly black homebuyers.

Federal agents say a co-defendant, Jeremy D. Parady, told them that some or all of the men accused in the arson, including Walsh, met in the parking lot hours before setting the pre-dawn fires Dec. 6.

Six months later, Parady has pleaded guilty in the case, and Walsh and three other men are facing trials, the first of which is set to begin July 12. Parady has acknowledged that race played a role in his actions, but no single motive has been ascribed to all the alleged participants.

Rather, some law enforcement officials said, a variety of aims appear to have found expression in a single act: the destruction of a dozen half-million-dollar houses under construction at the Hunters Brooke subdivision in Indian Head.

"I think everybody had their own motives, including those who just like to set fires," Charles Sheriff Frederick E. Davis said.

Six men ages 20 to 22 were arrested in rapid succession beginning 10 days after the conflagration. Charges against one man, Michael E. Gilbert, were dropped eventually. His attorney has said Gilbert has made no agreement to cooperate with prosecutors.

Walsh's lawyer, William B. Purpura, said his client "immediately and continually denied" any involvement. Attorneys for the remaining defendants -- Michael M. Everhart, Roy T. McCann and Aaron L. Speed -- declined to comment.

According to law enforcement affidavits, all of the suspects but Walsh implicated others and, to varying degrees, incriminated themselves during interviews with investigators. A federal judge threw out a written statement investigators took from Speed, whose case is scheduled to be heard first, saying that Speed was improperly questioned after invoking his right to counsel.

The suspects come from four towns in two counties, but some have connections that go back years: Parady and Speed attended elementary school together in Waldorf. Speed and Everhart attended the same high school, also in Waldorf, at the same time.

Others are linked through their interest in cars and in the Wednesday-night gathering, informally called "the car show," which drew people from as far away as Montgomery County. Gilbert allegedly told investigators he was a member of the Unseen Cavaliers. Gilbert's girlfriend, April Wilkinson, said three suspects -- Everhart, McCann and Parady -- also appeared regularly at the gatherings.

Yet there were tensions among them as well. In September, Parady alleged in court that McCann and Walsh had threatened him. A judge ordered McCann, but not Walsh, to stay away from Parady until March. Parady's sister has said her brother and Everhart, once inseparable, have recently become estranged.

Walsh was quoted in a Bureau of Alcohol, Tobacco, Firearms and Explosives report as saying that he had worked in pyrotechnics at an amusement park. He also posted online prolifically before his arrest, sometimes composing poems that evoked themes of love and loss. In a lighter moment, using the screen name WebPhantom99, he wrote that his hobbies include "anything that will keep me occupied and entertained without putting me in a nice set of matching steel bracelets."

Parady, at the time of his arrest, was a probationary member of the Accokeek Volunteer Fire Department. Speed, whose bid to become a volunteer at another fire department was rejected, worked as a security guard for a company hired to guard Hunters Brooke. According to a law enforcement affidavit, Gilbert told investigators that, in his job at a roofing supply company, he had delivered material to the site on several occasions.

Determining motive has been among the most vexing aspects of the case for investigators. At a news conference in January, more than two weeks after the arrests, Davis offered a blunt assessment: "I have no idea what [the crime] is about," he said. "Who knows what people are thinking when they do something like this?"

Initially, attention focused on the possibility of eco-terrorism, because environmentalists had protested the development's effect on nearby wetland. That theory gave way to more personal avenues of investigation when agents learned that Speed allegedly felt mistreated by his employer after the death of his infant son, a twin who succumbed to an illness.

Prosecutors have said that some of the suspects have referred to the arsons as "Operation Payback." The ATF report quotes Walsh as first saying the "operation" was a prank involving toilet paper, then saying it involved "blowing up a vehicle."

Some Charles officials now say that understanding the fires requires knowing the county, where affluent black newcomers are fast turning what was farm country into a Washington suburb brimming with almost 137,000 residents. The number of black residents jumped 70 percent between 1990 and 2000, and was estimated in 2003 at more than 39,000.

Candice Quinn Kelly, a county commissioner, likened the arson to the church bombings and other atrocities of the civil rights era, crimes motivated by racism but even more, she said, by fear "of change that people were not ready to accept.

"That was fear of a loss of power and control and of a way of life you've held onto, and that's what makes people do things that they know are wrong and that they regret," she said, stressing that even the most anti-development segment in the county condemned the fires at Hunters Brooke.

When he pleaded guilty in April, Parady said the Hunters Brooke development was targeted because a large number of black people were buying houses there. According to a law enforcement affidavit unsealed earlier, Parady had told investigators that Walsh and Speed also set the fires for racial reasons. That affidavit quoted Parady as saying that Speed complained before the fires that the "neighborhood is going black" and that Walsh helped in the fires because he "doesn't like black people at all."

Edith J. Patterson, the county's first African American commissioner, said the suspects are "people who are afraid of change." She added: "And like many other counties, Charles is one that is going through transition."

According to the same affidavit, Gilbert offered investigators another motive: that the fires were intended to raise the profile of the Unseen Cavaliers, a group that the affidavit says is also known as the Family. Gilbert told investigators Walsh approached him with "a plan to make the Family bigger and more famous," the affidavit states.

Assistant U.S. Attorney Donna Sanger endorsed that possible motive during a court hearing in December, saying Walsh and his associates wanted "to make a name for the Family, and they wanted to do something big.

"He had this fascination with fire, and he focused on the Hunters Brooke development as the place where he wanted to make this statement," Sanger said. "He is the one who settled on the means, the method and the target."

Capt. Joseph Montminy of the sheriff's office said he believes crime often is less complex than it appears and can be simply the chance product of a group's dynamic. "They all happened to be together at one place to formulate this plan," he said, referring to the Denny's restaurant where Walsh allegedly hatched the plot. "Had a couple of them been bowling or doing something else that night, this may not have happened."

The Unseen Cavaliers were absent from the parking lot outside Wendy's last week, but several dozen young people had gathered less than a mile away, in front of a Burlington Coat Factory in a strip-mall parking lot. As thumping bass mixed with the roar of unmuffled engines, some groused that authorities had cracked down since the fires in Hunters Brooke.

"We're just a bunch of kids trying to stay out of too much trouble," said a man who refused to give his full name, adding later, "There's nothing else to do here."

Soon, two sheriff's cruisers rolled into the parking lot, police dogs barking in their back seats. The young people scrambled into their Camaros and Mustangs -- their Cavaliers, too -- and peeled out of the parking lot, roaring into the night.

Staff writers Ruben Castaneda and Amit R. Paley and staff researcher Bobbye Pratt contributed to this report.

Bucky Bowling, left, and Tom Wathen of Southern Maryland Electric Cooperative and builder Tim Schwartz survey electrical damage in December. Sketch of Patrick S. Walsh Jeremy D. ParadyMichael M. EverhartAaron L. Speed