The Tsarnaevs' deadly brotherhood: Column

• How could these young men have ruthlessly murdered and maimed spectators at the Boston Marathon%3F
• The key to motivation may lie not just in some anti-American sentiment but in the brotherly bond itself.
• Time and time again%2C we have seen horrible crime sprees perpetrated by partnerships.

By all accounts, Dzhokhar Tsarnaev, the younger of two brothers suspected of having perpetrated the Boston Marathon bombings, was a good kid, a bright young man and hardly the type of angry malcontent you'd expect of a terrorist. He graduated from the prestigious Cambridge Rindge & Latin School, where he starred on the varsity wrestling team; was named student-athlete of the month in his senior year; and earned a $2,500 scholarship from the city of Cambridge toward his tuition at University of Massachusetts-Dartmouth. One friend even characterized the 19-year-old as a guy who gave off "a good vibe."

Dzhokhar's older brother, Tamerlan, seems to have had a far less glowing past. The 26-year-old community college dropout had been arrested on charges of domestic violence. In recent years, according to relatives, he had grown increasingly religious, drawn to a more observant Islam and possibly anti-American ideology. By his own account, Tamerlan had felt friendless here in America.

Few early clues

Despite all this, Tamerlan showed little indication of having the potential or the desire to commit an extreme act of mass violence, and was cleared in an FBI investigation two years ago. Friends and neighbors were unconcerned. Tamerlan's boxing coach, for example, described him as a nice guy and a piano player who often brought his younger brother to boxing practice.

Given their fairly unremarkable lifestyles and reputations, why would the Tsarnaev brothers have allegedly engaged in such diabolical crimes? How could these young men have heartlessly murdered and maimed spectators at the Boston Marathon and days later fatally shot an officer of the Massachusetts Institute of Technology?

The key to motivation could lie not just in some anti-American sentiment but also in the brotherly bond itself. Individually, neither might have been prone to murder, but in partnership they brought out the very worst in each other, both in ideology and behavior. Living together for years, they would have reinforced whatever negative beliefs they had about the American way of life. Tamerlan might have felt friendless in America, but he surely had an eager and devoted disciple in brother Dzhokhar to share ideas and plans.

Arguably, these crimes would not have taken place were it not for the close brotherly connection. Indeed, it is far easier to do despicable things when others join in. No matter how deeply committed each is to the cause, participation in itself helps support and justify the mission.

Time and time again, we have witnessed horrible crime sprees born out of partnerships — joint ventures involving brothers, cousins, spouses and other family relations.

Bonded in crime

In the late 1970s, brothers Gary and Thaddeus Lewingdon murdered 10 victims in Ohio. About the same time,Gerald Gallego and his wife, Charlene, kept a series of sex slaves in California, eventually killing them. In the same state, meanwhile, cousins Angelo Buono and Kenneth Bianchi raped and tortured 10 women and girls in the "Hillside Strangler" murders. Brothers Bruce, Norman and David Johnston operated a crime ring in Pennsylvania from the mid-1960s through the next decade, executing those they suspected might rat to the FBI.

Washington, D.C., snipers John Muhammad and Lee Malvo shared a pseudo father-son relationship. And, of course, the followers of Charles Manson and other cult leaders would do anything for their father figures. In each situation, the real or quasi family tie was critical for the murder sprees.

The leader, which in last week's bombings undoubtedly was the older suspect, is emboldened by the admiration of his protégé and "foot soldier." The follower finds inspiration in the praise and approval of his mentor.

Whatever the motive for murder, each participant benefits psychologically from the sense of camaraderie and solidarity.

At the end of the day, literally, Dzhokhar Tsarnaev surrendered to the police after being discovered hiding in aboat just beyond the search perimeter. Without his older brother around, he was far less formidable a foe for the police. He wasn't strapped with explosives as his brother had been. On his own, Dzhokhar had little fight left or reason to continue.

It is very easy to describe the marathon bombers as monsters, and unquestionably their deadly deeds were monstrous. Although many people with good reason have referred to the suspects as "animals," understanding (without justifying) the brothers' motivation requires us to examine basic human needs for belonging and respect that are sometimes fed through criminal partnerships.

James Alan Fox is the Lipman Professor of Criminology, Law and Public Policy at Northeastern University in Boston and author of The Will to Kill: Making Sense of Senseless Murder.

In addition to its own editorials, USA TODAY publishes diverse opinions from outside writers, including our Board of Contributors.

* This column has been updated to reflect the print version of the April 24 edition.