The penalty phase of the trial of convicted Boston Marathon bomber Dzhokhar Tsarnaev began on April 21.
The jury will decide whether the 21-year-old Tsarnaev will be sentenced to death or to life in prison without possibility of parole.
Three people were killed and more than 260 wounded when two bombs exploded at the finish of the marathon on April 15, 2013.
In her opening statement, prosecutor Nadine Pellegrini said Tsarnaev was "unconcerned, unrepentant and unchanged" two years after the attack.
She told jurors that the death penalty is "appropriate" because Tsarnaev "planned and plotted to kill."
The defense has argued that Tsarnaev was strongly influenced by his radicalized older brother, Tamerlan, who was killed in a gunfight with police days after the attack.
Public opinion polls in Boston show most residents oppose sentencing Tsarnaev to death.