The jury that convicted Boston Marathon bomber Dzhokhar Tsarnaev has begun deliberating whether he should be sentenced to life in prison or execution by lethal injection.
Jurors retired to consider Tsarnaev's fate after federal prosecutors made their final impassioned arguments that he should be put to death and his lawyers asked for mercy.
Death or life in prison without parole are the only two options for the jury, which last month found Tsarnaev guilty of all 30 federal counts against him over the bombing on April 15 2013. Seventeen of those counts carry the death penalty, but the jury must reach a unanimous decision for it to be imposed.
Three spectators were killed and more than 260 others injured in the attacks near the marathon finish line.
During the four-month trial, prosecutors have portrayed Tsarnaev as a callous, unrepentant terrorist who carried out the deadly 2013 attack with his radicalised older brother, Tamerlan. They are demanding the death penalty.
Tsarnaev's lawyers admitted he participated in the bombings but told the jury he was "a good kid" who was led down the path to terrorism by Tamerlan, who wanted to punish the US for its actions in Muslim countries. They have asked the jury to spare his life, saying he was 19 at the time.
The defence showed the jury photos of the federal Supermax prison where Tsarnaev likely would be sent if he is sentenced to life.
His lawyers said he would remain locked in his cell 23 hours a day, living an austere, solitary existence until the day he dies - denying him the martyrdom he apparently wanted.
Prosecutors, however, said death is the only appropriate punishment for Tsarnaev. They said he was an equal partner with his brother in planning and carrying out the bombings. He planted his bomb behind a group of children, killing eight-year-old Martin Richard.
"Nothing will explain his cruelty and his indifference," prosecutor Nadine Pellegrini said.
US District Judge George O'Toole Jr sent the jurors home after 45 minutes of deliberation.
They will reconvene tomorrow.