Boston bombings: How did Dzhokhar, Tamerlan Tsarnaev decide to kill?

A jury sentencedDzhokhar Tsarnaev, 21, to death by lethal injection for his role in the deadly 2013 Boston Marathon bombings. CBC's Paul Hunter delves into the past ofDzhokhar and his brother Tamerlan, who died during a gun fight with authorities, to gleanwhat makes a killer.

• How events unfolded during the Boston Marathon bombing
• Dzhokhar Tsarnaev sentenced to death

The brothers grew up in Chechnya before unrest forced them to flee to Krgyzstan.

In 2002, the family moved to Cambridge, Mass., andseemed to embrace the American dream. Their parents envisionedTamerlan as a boxer for the American Olympic team and Dzhokharstudying at an esteemed institution like Harvard University.

But those dreams remained distant, and Tamerlanremained an outsider unable to box for America thanks to a rule change, unemployed and married with a child. A frustrated Tamerlan went back to visitDagestan.

Meanwhile, Dzhokharearned poor grades and massive debt in college.

When Tamerlan returned from Dagestan, he reconnected with his floundering younger brother, and the pair made plans to detonate bombs at the Boston Marathon finish line.

Watch Paul Hunter's documentary at the top of this story to learn more about the brothers behind the bombings.