Dzhokhar Tsarnaev, who was found guilty on Wednesday of the 2013 Boston Marathon bombing that killed three people and injured 264 others, may face the death penalty if a jury decides that should be his fate.

Tsarnaev, 21, is the surviving member of pair of ethnic Chechen brothers who planted the homemade pressure-cooker bombs that tore through the crowd at the famed race’s finish line in one of the most shocking attacks on US soil since September 11, 2001. He left a note behind describing the attack as an act of retribution for US military campaigns in Muslim-dominated countries.

Convicted Boston bomber Dzhokhar Tsarnaev.

His lawyers opened Tsarnaev’s federal trial in Boston a month ago by bluntly admitting “it was him” who planted one of the bombs on April 15, 2013 and three days later shot dead a police officer, kicking off a day of chaos in Boston.

After 11 hours of deliberations over two days, the jury found him guilty of all 30 criminal counts he faced.

The slightly built, lightly goateed defendant stood silently, shifting uncomfortably as a US District Court official read out each guilty finding, a process that took 25 minutes.

The courtroom was packed with survivors of the attack including the parents of eight-year-old Martin Richard, the youngest fatality, and law enforcement officials, including former Boston Police Commissioner Ed Davis.

After the verdict was read, Karen Brassard, whose left leg was badly injured by one of the bombs, said she was glad that Tsarnaev had shown no emotion.

“Personally I wouldn’t have bought it if he had,” Brassard said, as an early-spring sleet fell over Boston’s waterfront. “He has been, to use my word, arrogant walking in and out of the courtroom.”

He has been arrogant walking in and out of the courtroom

The blasts killed restaurant manager Krystle Campbell, 29, Chinese exchange student Lingzi Lu, 23, and Richard. Tsarnaev also was found guilty of the fatal shooting of Massachusetts of Institute of Technology police officer Sean Collier, 26.

With Tsarnaev’s guilt established, the trial now moves into a second phase where prosecutors and defence attorneys will call another round of witnesses. The jury will decide whether to sentence him to death or life in prison without possibility of parole. That phase begins next week.

Tsarnaev’s lawyers have indicated that they plan to show that his 26-year-old brother Tamerlan was the driving force behind the attack, a contention they hope will persuade the jury to spare his life.

In a stark contrast to defence attorney Judith Clarke’s opening-statement admission of Tsarnaev’s guilt in placing the bombs, she turned her attention during last week’s closing argument to the making of the bombs.

“Tamerlan did that,” Clarke said, contending that without the older brother there would have been no attack. Tamerlan died early on April 19, 2013, after Dzhokhar ran him over with a car while fleeing a gunfight with police.

The amount of time spent in the jury room suggests the jurors were thorough in considering the charges, said David Weinstein, an attorney in private practice who in prior jobs as a state and local prosecutor brought death-penalty cases.