In this courtroom sketch, Dzhokhar Tsarnaev, second from left, is depicted standing with his defense attorneys as the jury presents its verdict in his federal death penalty trial on April 8, 2015, in Boston, US. [Photo/IC]

BOSTON - Dzokhar Tsarnaev was found guilty on Wednesday of the 2013 Boston Marathon bombing that killed three people and injured 264 others, and the jury will now decide whether to sentence him to death.

Tsarnaev, 21, is the surviving member of pair of ethnic Chechen brothers who planted the homemade pressure-cooker bombs that tore though the crowd at the famed race's finish line in one of the most shocking attacks on US soil since Sept 11, 2001.

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 8-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."

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.