Boston Bomb Accused 'Had Murder In His Heart'
In the much anticipated trial's opening statements on Wednesday, federal prosecutors said the accused had wanted to "tear people apart and create a bloody spectacle".
Tsarnaev, 21, wearing a white shirt without tie, and a blazer, stared straight ahead as the case against him was laid out amid tight security at the US District Court in Boston.
The defence made a surprising admission, acknowledging the accused's guilt.
But they argued that he was heavily influenced by his 26-year-old¬†brother, Tamerlan Tsarnaev.
Prosecutors say the Tsarnaevs placed two pressure-cooker bombs near the marathon finish line on 15 April 2013, killing three people and injuring 264 others.
The younger Tsarnaev denies 30 charges, including the killing of a police officer days after the attacks.
The parents of the youngest victim, eight-year-old Martin Richard, were among a dozen or so victims in court.
Heather Abbott, a dancer, and Marc Fucarile, both of whom lost legs in the blasts, also attended the hearing.
Assistant US Attorney William Weinreb painted a picture of the carnage wreaked by the attacks, describing how the "air was filled with the smell of burning sulphur and people's screams".
"The defendant wasn't there to watch the race," said Mr¬†Weinreb. "He had a backpack over his shoulder and inside that backpack was a homemade bomb.
"It was the type of bomb favoured by terrorists because it is designed to tear people apart and create a bloody spectacle.
"He pretended to be a spectator, but he had murder in his heart."
He said¬†Tsarnaev and his brother carried out the attack to punish the US for military actions in Muslim countries.
"He believed that he was a soldier in a holy war against Americans,"¬†Mr Weinreb told the court.¬†
Defence lawyer Judith Clarke told the jury in her opening statement: "It was him."
But she added: "It was Tamerlan Tsarnaev who self-radicalised. 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."
Tamerlan Tsarnaev was inadvertently run and over and killed by his younger brother days after the bombings as he tried to flee police during a shoot-out.
His widow is under investigation and could face charges related to the bombings, US media report.
The younger Tsarnaev was found four days after the bombings hiding in a boat parked in the backyard of a home in the Boston suburb of¬†Watertown.
A panel of 10 women and eight men will decide whether Tsarnaev, an ethnic Chechen who arrived from Russia more than a decade ago, is guilty.
They will also determine whether to sentence him to death or life in prison without possibility of parole.