One of the first things Tsarnaev's attorney Judy Clarke told the court Wednesday was that he was responsible for the "senseless, horrific, misguided acts." The defense would only contest the "why" of it all, she said, indicating it was Tsarnaev's late older brother, Tamerlan, who pushed her client down the dark path.
All day the defense did not cross examine witness after witness from the prosecution while they recounted the horror of that April 15, 2013 day when three were killed -- including an eight-year-old boy -- and 260 injured after dual explosions ripped through the crowds near the finish line of the Boston Marathon.
The defense's move surprised many federal officials who said today they are asking why a court should spend potentially months proving what the defense has already admitted.
Legal experts told ABC News that while the defense's strategy may appear odd from the outside, that's only because they're not focusing on winning this phase of the trial, but avoiding the death penalty later.
"Given the amount of evidence the government has, I would suggest it's the only strategy," said Robert Bloom, a Boston College law professor. "I think their objective is to develop a rapport with the jury. They certainly don't want to go and cross examine victims very hard. By developing a rapport with the jury, when their turn comes to talk about the death penalty phase of it, they will have a rapport with the same jurors that are hearing all this evidence."
Charles Ogletree, Professor of Law at Harvard Law School, agreed.
"Their point is there's no question that what he did was wrong, being involved in the marathon bombing, but they're also saying that life imprisonment is enough punishment that would appropriate," he said.
So why not just plead guilty to the 30 charges related to the bombing in the first place?
First, Olgetree said the defense likely lobbied for a deal in which Tsarnaev pleaded guilty to avoid the death penalty, but the government didn't go for it -- potentially under pressure from the Obama administration, after Attorney General Eric Holder authorized the government to seek the death penalty last January.
"So they don't think life imprisonment is justified, is not enough," Ogletree said.
"They're not taking the death penalty off the table for [Tsarnaev]," ABC News legal analyst Dan Abrams said on "Good Morning America," noting that in most cases prosecutors would have gone for such a deal.
So there was little incentive for the defense to plead guilty now.
Second, Bloom said that by pleading not guilty, the defense is preserving its right to an appeal should it choose so later on.
Ogletree said he thinks the defense's strategy is a good one and that they will accomplish what they set out to.
"I think it's a strategy that's going to work," he said. "Now that you're going to trial, having to make sure that [you're] looking around and you're saying that my client is guilty of what he's done. He's guilty of his crimes. And he needs to be punished. The punishment has to fit the crime... Life imprisonment is a very serious punishment."
Graphic, Emotional Testimony
As Tsarnaev sat impassively in court Wednesday, the court was shown for the first time new videos from the day of the blast.
One, shot by a bystander, showed the horror and chaos in the immediate aftermath of the blasts, as emergency responders attempted to prioritize those who needed help the most and family members frantically searched for their loved ones. Another video from inside a nearby sports store showed people ripping clothes of the racks to use as makeshift tourniquets for the injured.
"It's hard reliving the situation, and the circumstances that happened that day, when we mentioned the ones that we lost that day, the ones that really should be remembered," said Marc Fucarile who was at the race.
Similar testimony is expected today, potentially with other new videos that captured the horrific event.