The four people who were killed in the Boston Marathon bombing and the subsequent manhunt (clockwise from top left): Martin Richard, Sean Collier, Krystle Marie Campbell and Lu Lingzi

The first day of the sentencing phase of the Boston Marathon bombing trial began on 21 April, with the prosecution bringing up several witnesses and video of one of the victims. Prosecutors will spend the second phase of the trial trying to convince the jury that convicted bomber Dzhokhar Tsarnaev should receive the death penalty.

The Boston Globe reported that the brother of victim Krystle Marie Campbell took to the stand to talk about his sister and the impact her death had had on their family. "It's still tough. It's still tough," William Campbell III said. "We still think about her. Not a day that goes by that she doesn't pop in your head."

Gillian Reny, who was injured during the bombing, spoke about her leg injury and her subsequent hospital stay. "My leg was almost completely torn apart," Reny said, according to the Los Angeles Times. "I was in shock and had nothing to stand on."

"My body crumpled to the ground... I was terrified I was going to die," she continued. The aspiring dancer was kept in a two-day medically induced coma before her leg-saving surgery.

According to the LA Times, prosecutors also displayed a never-before-seen photo of Tsarnaev giving a surveillance camera the middle finger. "This is Dzhokhar Tsarnaev," Assistant US Attorney Nadine Pellegrini said. "Unconcerned, unrepentant and unchanged. Without remorse, he remains untouched by the grief and the loss he caused."

Sentencing phase to last at least four weeks

Tsarnaev was found guilty of all 30 federal counts relating to the bombing and subsequent manhunt earlier this month. ABC News reported that the 21-year-old is not expected to take the stand in the defence's attempt to save him from the death penalty.

The convicted bomber was found guilty of killing three and injuring more than 260 people using two pressure-cooker bombs during the 2013 Boston Marathon. Tsarnaev and his brother Tamerlan, who died four days after the marathon in a police shoot-out, also killed an MIT police officer as they attempted to evade police.

The trial's sentencing phase is expected to last at least four weeks. The jury must decide whether Tsarnaev will be sentenced to death or spend his life in prison without a chance for parole.