Mass murderers are as different as their killing field âÄî be it a nursing home or a suburban home âÄî and as diverse as their reasons for killing âÄî whether it’s spousal betrayal or the loss of a job. But experts say most people who embark on such wholesale slaughter share certain key characteristics: A catastrophic event that triggers a suicidal rage and an unquenchable thirst to get even. And there is often no way to see it coming. “I’m not sure you can even predict it,” says Mark Safarik, who retired in 2007 as a senior profiler in the FBI’s famed Behavioral Analysis Unit. “It’s the constellation or coming together, the perfect storm of someone’s last shot at something. For them, there’s just no other way out. Or if there’s another way out, they don’t choose it, because they’re going to punish somebody.” Mass murder is nothing new, and the invention of repeating guns only made it easier. But even experts who study the phenomenon have been stunned by the recent rash âÄî seven in the past month, three in the past week alone. “Boy, this is a lot,” said Safarik, now a partner with Forensic Behavioral Services International. Criminologist Jack Levin was not surprised to learn that the man who shot up a Binghamton, N.Y., immigrant center on Friday had recently been laid off from his job at a vacuum cleaner factory. What puzzled him at first was why Jiverly Wong chose his target. “If it was only the job loss, why didn’t he go back to the work site and kill his manager and his co-workers?” the Northeastern University professor asked himself. “Because that’s what we’re used to seeing when someone is set off by a termination at work. But he didn’t do that.” Then he learned that the 41-year-old Wong âÄî an ethnic Chinese man raised in Vietnam âÄî had taken English classes at the American Civic Association, and that he blamed his inability to find and keep work, in part, on his poor language skills. That’s when the massacre began to make sense âÄî or as much sense as any such tragedy can. Wong’s personal failures meant that he had “lost the respect in the eyes of others of the immigrant community,” said Levin, co-author of the book “Extreme Killing: Understanding Serial and Mass Murder.” “I’m sure that he was on a suicidal rampage, but first he decided he was going to get even,” Levin said of Wong, who killed 13 before ending his own life. “And just like every other mass killing I’ve studied, his motive âÄî his primary motive âÄî was revenge.” New clues emerged Monday in a letter purportedly written by Wong and mailed to a television station on the day of the massacre. In it, the gunman said he was persecuted by police, couldn’t accept his “poor life” and was intent on killing himself and at least two other people. Wong’s attack came less than a week after a rampage that killed eight in a North Carolina nursing home. And it preceded attacks in Pittsburgh and Washington State that left three police officers and five children dead. Media coverage of such events blankets the airwaves, and that becomes another factor, Safarik said. In this era of saturation coverage, mass murders seem to beget more mass murders, and the stumbling economy only makes matters worse. “I think that people that are on the edge, that are contemplating such tragic events, sometimes all it takes is that being highlighted in the media for them to go, ‘You know? I could do something like that, I’m THAT angry,'” said Safarik. “It’s in their face on the television, and now it’s in their thinking pattern. “It becomes an option that, perhaps earlier on, wasn’t an option for them.” Most mass murderers, like most serial killers, are middle-aged, white males, like Robert Stewart âÄî the man who walked into Pinelake Health and Rehab in Carthage, N.C., on March 29 in an apparent search for his estranged wife. But that profile, coupled with the large body count, is where the similarities seem to end. Serial murderers often kill for sadistic pleasure, said professor James Alan Fox, a colleague of Levin’s at Northeastern and his co-author. Mass killers, on the other hand, tend to externalize their homicidal reasonings. “They always think someone else is to blame. ‘My boss doesn’t give me the right kinds of assignments. My co-workers don’t do enough to help me succeed. My wife doesn’t understand me at all, doesn’t treat me with respect.'” Serial killers want the death to go on and on, and they work hard not to get caught, Fox said. But for mass murderers, their own death is a virtual certainty, and they want to take as many with them as possible. “Before they die, it’s very important for them to get some satisfaction, to get even with the people or the institutions or the world that has treated them so badly or made their life so miserable.” Fox and Levin say mass killers fall generally into three categories: âÄî People who are angry at a specific person or group of people and who selectively target those individuals. âÄî People who are angry at a place âÄî like city hall âÄî or a group âÄî like immigrants âÄî and kill anyone who happens to represent those things. âÄî And, the rarest type, people who target victims at random, such as he sniper who killed 16 and wounded 31 from the tower of the University of Texas administration building in 1966. That most of these killers are male should come as no surprise: 93 percent of violent crimes are committed by men, Safarik said. Fox offers several explanations for this gender gap. First, women tend to blame themselves for their failures and, so, more often simply commit suicide. Also, men tend to have better access to guns and firearms training. And while women generally see violence as a means of defending themselves or their loved ones, Fox said many men view force as an “offensive weapon.” “Men will often use violence to show them who’s boss, to assert control,” Fox said. “So if a guy gets fired, he goes back to work and he says, ‘You think you fired me? I’m firing you âÄî literally.'” Men are also more likely to define themselves by their jobs and their earning capacity, Fox said. In the case of Wong, his frustration was compounded by his inability to master English, which he appears to have blamed on the immigrant center. “The American dream for him was a nightmare,” said Fox. “The land of opportunity, for him, was a cruel joke.” Typically, mass murderers have no criminal record or history of psychiatric treatment, Levin said. That would describe Stewart. Before he walked into the Pinelake rehab center two Sundays ago, the 45-year-old disabled house painter’s only real brush with the law was a drunken-driving charge in the late 1980s. The apparent object of Stewart’s rage, estranged wife Wanda Luck, was supposed to have been working on the main floor the day of the shootings. But through a quirk of fate, she was assigned to the Alzheimer’s wing, which was behind a locked, password-protected door. Had Stewart walked in and immediately found Luck, might the shooting have stopped there? It’s possible, Fox said, but unlikely. “Once they start shooting, the rage continues,” he said. Virginia Tech student Seung-Hui Cho also had no criminal history, aside from the odd speeding ticket. But there were plenty of people who sensed he was a ticking time bomb. In her new book, “No Right to Remain Silent: The Tragedy at Virginia Tech,” former English department chairwoman Lucinda Roy writes of her attempts to tutor Cho after his disturbing behavior and macabre writing got him kicked out of class. During their sessions between October and December 2005, Roy described Cho as someone from whom sadness oozed “like the smell of smoke from a nicotine addict.” Sitting with Cho between her and the office’s only exit, Roy felt as if she were talking with “an inanimate object.” “The core of his identity is impenetrable,” she wrote of the Korean native, “his gaze strangely neutered, as if he has spent his entire life ridding it of expression.” Roy was frightened for herself and for Cho. But she could not have predicted what was to come. Initially considered more a suicide risk, Cho was ordered to undergo outpatient counseling, but apparently no one followed up. His anger and feelings of isolation festered until April 16, 2007, when the self-described “boy named LOSER” went on a campus killing spree that left 33 dead âÄî including himself. In a recorded manifesto mailed to the media after he killed his first two victims, Cho lashed out at the “brats” and “snobs” with their trust funds, fancy cars, jewelry and cognac. Like Columbine (Colo.) High School killers Eric Harris and Dylan Klebold, to whom he dedicated his slaughter, Cho declared that he was wreaking revenge for countless slights and indignations âÄî real or imagined. “You had a hundred billion chances and ways to have avoided today,” the 23-year-old snarled into the camera lens. “But you decided to spill my blood. You forced me into a corner and gave me only one option. The decision was yours.” In many cases, there are warning signs of impending attacks that go unrecognized or ignored. But often, Levin said, it is virtually impossible to know that someone bent on suicide has decided to take others with them. Like Wong, hundreds of thousands of Americans have been laid off in recent months. And Stewart, who was taken alive, is not the first man whose wife has left him. Many other people “have all these symptoms, but they never get the disease,” Levin said. “They may blame other people for their problems. They may be isolated so they have no support systems in place. And, yet, they don’t hurt anybody.”