The jury, made up of seven women and five men, all white, will weigh 30 counts against Mr. Tsarnaev, including whether he used a weapon of mass destruction. The jurors are all but certain to find him guilty on most counts. After they return their verdict, the same jurors will move on to a second phase, in which they will decide whether to sentence him to death or to life in prison.

In their closings, the prosecution and defense lawyers squared off more sharply against each other than they did in their openings.

The government depicted Mr. Tsarnaev as an intellectually and emotionally committed jihadist, bent on getting even with the United States through the premeditated killing of innocent women and children “because he wanted to make a point,” Mr. Chakravarty argued. “He wanted to terrorize this country.”

Mr. Chakravarty said Mr. Tsarnaev picked a spot on Boylston Street near the marathon finish line that was especially crowded with children, including the Richard family, and stood there for four minutes, deliberately planting the bomb near them. Martin Richard, 8, was among the three people killed.

Ms. Clarke sought to deflate that theory, saying that Mr. Tsarnaev had picked that spot because it was near a tree, which she implied he selected as a marker, not to target children. “It does not make it better, but let’s not make his intent any worse than it was,” she said.

In a rebuttal by the government, the lead prosecutor, William Weinreb, noted that Ms. Clarke had said she was not trying to shirk Mr. Tsarnaev’s responsibility for his crimes but said in fact she was doing just that. “It’s an attempt to sidestep responsibility, not to take responsibility,” he said of the defense strategy of blaming Tamerlan.

The two sides were in essence laying the foundation for the next phase of the trial. The government insisted that Mr. Tsarnaev was a full and equally guilty partner with his brother — and by unspoken extension, deserved to be put to death for his heinous actions — while the defense argued that he was less culpable and, by unspoken extension, deserved to be spared of the death penalty.

The jury, somewhat bleary-eyed, particularly after the judge’s lengthy instructions, went home at the end of the day and is to begin deliberations Tuesday morning.