The sentencing phase in the Boston Marathon bombing trial began on Tuesday as prosecutors began making their case as to why convicted terrorist Dzhokhar Tsarnaev should be put to death.

Earlier this month, Tsarnaev was found guilty of 30 charges for his role in the 2013 Boston Marathon bombings, including conspiracy to use a weapon of mass destruction and bombing a public place. The charges also covered a carjacking that took place in the aftermath of the attack, the deadly shooting of a Massachusetts Institute of Technology police officer, and a gunfight in Watertown, Massachusetts, in which Tsarnaev and his deceased brother tossed explosives at police.

During the trial, defense lawyers argued that Tsarnaev participated in the attack that killed Richard and two others on April 15, 2013 because he was under the influence of his older brother, Tamerlan, who then died during a shootout with police three days later.

Now, it is up to the same jury to decide whether Tsarneav should face life in prison or death.

On Tuesday, prosecutors showed the jury a photo of Tsarnaev holding up his middle finger to a security camera in his jail cell just three months after the attack, reports The New York Times.

"This is Dzhokhar Tsarnaev -- unconcerned, unrepentant and unchanged," Nadine Pellegrini told the jurors, according to The Associated Press. "He had one more message to send," the prosecutor said.

The government then called their first witness to the stand -- a woman named Celeste Corcoran who lost both of her legs in the attack. During her testimony, she decribed the excruciating pain she felt following the blast.

"I remember hearing just blood-curdling screams. I just remember looking around, just seeing blood everywhere, sort of like debris falling from the sky," Corcoran said.

Corcoran said her husband acted quickly by applying pressure to her legs. He also used belts to tie tourniquets.

"I just remember thinking how awful this was and how this had to stop. This couldn't be real, couldn't be real," she said.

"Then I was saying, 'Hell, no, I can't die,'" she added. "'I have to be there for my kids. I have to be there for my husband. I have too much living to do. Don't let this be the end. How can this be the end?'"

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