Defence attorney Judith Clarke told the United States District Court in Boston that Tsarnaev, 21, who could face the death penalty, was a secondary player in the attacks that killed three people and injured 264 at the race on April 15, 2013, and the fatal shooting of Massachusetts Institute of Technology police officer Sean A Collier three days later.

She insisted Tsarnaev's actions had been influenced by his older brother, Tamerlan, who was killed when his younger brother unintentionally ran him over after a gun battle with police a few days after the bombing.

"It was Tamerlan Tsarnaev who self-radicalised," explained Clarke, who said she would not attempt to sidestep Tsarnaev's involvement in the attack.

"It was Dzhokhar who followed him.

"The evidence will show that Tamerlan planned and orchestrated and enlisted his brother into this series of horrific acts."

However, Assistant US Attorney William Weinreb had anticipated that the defence would try to blame Tamerlan and said the focus will be on the defendant as he is the one the Government has to prove guilty.

He claimed Tsarnaev had "murder in his heart".

"He believed that he was a soldier in a holy war against Americans," he added.

Dzhokhar Tsarnaev could face the death penalty ©Getty Images


The jury saw a number of videos of the bombs going off and the aftermath, while Weinreb gave a graphic account of the injuries caused by the pressure cooker bombs used by the brothers and described the finals moments of those that died - eight-year-old Martin Richard, 23-year-old Lingzi Lu and 29-year-old Krystle Campbell.

About two dozen victims of the attacks, among those were Richard's parents Denise and Bill, were present in the courtroom.

The trial, which is expected to last three to four months, will be split into two parts - the first to determine Tsarnaev's guilt or innocence, and the second to determine the punishment if he is convicted, with the jury to decide whether he is put to death.

The Boston Marathon bombing was the deadliest terror attack in the US since 9/11.

The Massachusetts city is now bidding to host the 2024 Summer Olympic and Paralympic Games.

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