Did a brotherly bond influence the Boston bombing suspects?

(CBS News) As investigators continue to learn more about the motivations behind suspected bombers Tamerlan and Dzhokhar Tsarnaev, some researchers point out that sibling psychology may have played a key role.

There have been a number of famous brothers in crime throughout history, including the three pairs of brothers who took part in the attacks on Sept. 11, 2001.

"When children are born, they're born into essentially what is a hothouse of influence; the older brother becomes the mentor to the younger brothers," Time magazine science editor Jeffrey Kluger said to "CBS This Morning: Saturday" co-hosts Margaret Brennan and Anthony Mason.

Special Section: Boston Marathon Bombing

The journalist is also the author of the book "The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us."

"It's true of of sisters too, but it's especially true in any same-sex pairing of siblings," he said. "The younger brother comes into the world needing the older brother, wanting the older brother for guidance."

With same-sex siblings, the default assumption is the older child will influence younger and that the skills learned from the older sibling makes the younger one want to be more like them by default.

Research shows that in behavior that involves a risk, such as criminal actions, there is an infectious nature to it, and it's more likely that a family member will mimic that harmful behavior.

However, Kluger explained that these types of dependencies are expected to phase out as children age, but in the case of the Tsarnaev brothers they might not have had that experience. This change in behavior is called "sibling moratorium," and it is a normal occurrence in healthy family relationships.

"By the time you get to college age, by the time you get beyond college, you've moved apart because you can't invest so much of your emotional energy and so many of your emotional calories into a member of your original family," he said. "When you are still in that situation with a same-sex, or even opposite-sex, sibling, you're not reaching out and into the world as you should be, and as a result you're stunting your emotional growth."

When the Tsarnaev family moved to the United States they were in a strange place and most likely experienced isolation, Kluger said. Then, as their parents, especially their father, left the U.S. they needed to rely more on each other, with Tamerlan taking a parental role as he was seven years older than Dzhokhar.

For the complete interview, click on the video in the player above


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