Two weeks ago, the jury in the Boston Marathon bombing trial found him guilty on all 30 charges he faced in connection with the deadly 2013 attack and its aftermath.
On Tuesday, the sentencing portion of the trial begins, and the jury will decide his punishment: life in prison with no parole or the death penalty.
Capital punishment remains a divisive issue in much of the U.S., particularly in recent months because of the publicity around botched executions, which has prompted certain states to review how they are done.
Thirty-two states have the death penalty and Massachusetts, where the trial is taking place, isn't one of them. Federal law allows for a death penalty and federal prosecutors can choose to pursue that course in certain cases, like Tsarnaev's, because he was charged with federal crimes.
Death sentences were carried out 35 times last year in the U.S. and more than 2,900 inmates were on death row.
But it's rarer for the death penalty to be sought and carried out in federal cases.
Seventy-one people were handed a death sentence between 1973 and 2013 in the federal system, according to the most recent statistics from the U.S. Department of Justice. Just three executions were carried out.
Tsarnaev could appeal a death sentence
If the 21-year-old Tsarnaev is given the death penalty, it wouldn't necessarily mean a swift execution as his legal team could appeal and that appeal could take years before all options are exhausted.
His lawyer, Judy Clarke, is trying to convince the jurors not to hand him the death penalty, and she has experience in this kind of thing. She successfully fought for the life of Ted Kaczynski, also known as the Unabomber, and has defended other high-profile clients.
In the first phase of Tsarnaev's trial the defence team previewed what their strategy will be during this second phase: they portrayed him as the vulnerable younger brother who was under the influence of his controlling older sibling Tamerlan, said to be the real mastermind of the bombing.
"The defence is going to be much more aggressive in putting on evidence that we haven't seen yet, making the point that this fellow was no more than a puppet responding to a puppeteer," suggests Roger Goldman, a professor at St. Louis University who has been watching the trial closely.
Another law professor monitoring the case, Daniel Medwed from Northeastern University in Boston, said the first part of the trial was about what Tsarnaev did, the second part is about who he is, his back story.
"What is he about, is there anything worth saving here? It's a different focus," Medwed explained.
Clarke is expected to highlight what are considered mitigating factors under the federal death penalty law and could argue that Tsarnaev acted under duress, that his role was minor and that he was mentally or emotionally disturbed.
Jury is open to idea of death penalty
On the other side of the courtroom, prosecutors will present evidence of the aggravating factors that can be considered under the law.
From the outset of the trial they said Tsarnaev fits the criteria for capital punishment, in that he committed offences that were particularly cruel, required substantial planning and resulted in the deaths of especially vulnerable people.
Three people died near the Boston Marathon finish line that day, one of them was an eight-year-old boy. A police officer also died during the manhunt for the Tsarnaev brothers.
The jury will weigh these aggravating and mitigating factors and make a decision. It has to be unanimous. "All it takes is one," said Medwed. "If one jury member is open to the idea that this person's life is worth saving then that's enough."
Even though Massachusetts hasn't executed anyone since 1947 and a majority of residents are against the death penalty, according to polls, the jury members aren't morally opposed to it. If they were, they wouldn't have been eligible to sit on the jury, according to the rules.
Medwed and other legal observers are speculating about what they will decide and why. The fact that they delivered a guilty verdict on every single charge, even minor ones, and that they did it so quickly could be clues.
Perhaps it signals they were moved by the prosecution's case and will be again in the second phase, said Medwed.
"The other school of thought, which I also embrace, is that this trial was a chance for the jury to vent and express their condemnation of what he did." Now that they have delivered the guilty verdicts, he said, the jury may feel life behind bars is suitable punishment and be more amenable to the defence arguments.