In all three cases, there were the almost predictable comments from casual acquaintances, characterizing the alleged gunman as a regular guy who kept to himself.

"I thought he was pretty nice," said a neighbor of Buford Furrow, a suspect in Tuesday's shootings at the North Valley Jewish Community Center in Los Angeles. "But then again, I knew that his beliefs were way out of line. They were good neighbors, but, well, I got blue eyes, so I guess that helps," the neighbor, Meda VanDyke, told the Seattle Times newspaper.

Other neighbors in eastern Washington state told the Seattle Times they regarded Furrow as a racist. One criminal justice professor across the country put him in the same category as convicted Oklahoma City bomber Timothy McVeigh and Benjamin Smith, a white supremacist who killed two people in the Midwest before killing himself last month.

All three, and others, were "freelancers or lone wolves who are incited by this incendiary language" in the white supremacy and Christian identity movements, said Harvey Kushner, chairman of the criminal justice department at Long Island University in New York.

Kushner said he and others who monitor hate crimes had been aware of Furrow for some time, and said he fit the profile of men who have committed such acts.

"They're predominantly white, they tend to be male, they tend to be Christian identity believers, which in no way reflects any teachings of mainstream Christian beliefs," Kushner said by telephone. "They tend to be failures in life and that tends to be the thread that runs through them."

Furrow surrendered to authorities in Las Vegas Wednesday after a gun assault Tuesday at the center, in which three children and two adults were wounded.

Less than a week before the Los Angeles attack, another solo gunman killed three people at two businesses in Pelham, Alabama. Acquaintances described the chief suspect, Alan Miller, as a "teddy bear."

A week before the Alabama deaths, day-trader Mark Barton killed his wife, two children and nine people at two brokerage firms in Atlanta before committing suicide. He was recalled as a Scout leader who loved his children.

The day-care shooting followed a lethal rampage by two high school students in Littleton, Colorado, last April. They killed 12 other students and a teacher before killing themselves.

William McDonald, a sociologist at Georgetown University who looks for patterns in these deadly events, said he found no overall pattern, but noted a pervasive view that these attacks might have been prevented.

"There's an awful lot of white males, but they're not always from the same class and they're not always the same age," McDonald said by telephone. "There's a little pattern in terms of race, and in gender -- no women are doing this."

The prevailing feeling that these kinds of men, some with histories of violence or uncontrolled anger, could be identified before they explode is impractical, McDonald said.

"People have a very unrealistic idea about making predictions about human behavior, even with very bizarre people," he said. "You can't pick them out with any degree of accuracy."

In the Littleton case, McDonald said, even with advance notice of some of the strange behavior of the two young gunmen, "That's not proof positive of anything, that they need to be locked up or drugged into zombies. The problem is there's no easy answer."

In the three recent cases, the issue of U.S. gun control law has surfaced even before the details of the crimes became known. Anti-gun groups like Handgun Control Inc. have cited them in their literature.

The National Rifle Association followed the Jewish center shooting case closely, and ran a headline on its Web site -- www.nra.org -- on Furrow's surrender to authorities minutes after the same news was broadcast on national television.

Despite a perception of worsening violence in the United States, the FBI reported earlier this year that the number of serious crimes dropped dramatically in 1998, the seventh straight annual decline.

And a U.S. government study released Tuesday found that although shootings at schools have commanded widespread media attention, the number of students expelled for bringing guns or explosives into schools dropped last year by 31 percent from the previous academic year.