A federal prosecutor told a jury Tuesday that Sayfullo Saipov, who killed eight people in a 2017 truck attack on a Manhattan bike path, was “a proud terrorist” whose actions merit “the most severe punishment the law provides” — the death penalty.

“He chose to come to this country and then fight for an enemy,” the prosecutor, Amanda Houle, said during the closing arguments of the penalty phase of Mr. Saipov’s trial in Federal District Court in Manhattan. The jurors in January convicted Mr. Saipov, a native of Uzbekistan, for carrying out the attack, which he has said was inspired by the Islamic State.

“When ISIS called upon him to fight overseas or attack here, he chose here — this city,” Ms. Houle said. “He chose to murder an innocent person and then he chose to do it again seven more times.”

She added: “Those are his choices, and he stands by them, so that is what brings us to this point.”

On Wednesday, the 12 members of the jury will begin weighing Mr. Saipov’s fate: whether to impose the death penalty or to sentence him to life imprisonment without the chance of release.

David E. Patton, a lawyer for Mr. Saipov, acknowledged in his summation on Tuesday that his client had caused pain and loss to victims and families that was “impossible to fathom.”

But he asked the jury to make “the appropriate moral decision” and spare his client.

“It is not necessary to kill Sayfullo Saipov,” Mr. Patton said. “It is not necessary to keep us or anyone else safe. It is not necessary to do justice. So we are asking you to choose hope over fear, justice over vengeance and, in the end, life over death.”

The clash over Mr. Saipov’s fate came nearly two months after he went on trial in Manhattan for the bike-path attack. In convicting him on Jan. 26 in the trial’s initial phase, the jury found Mr. Saipov guilty of all 28 counts he faced, including nine that carried a potential sentence of death.

Evidence showed Mr. Saipov used a rented truck and carried out the attack on Halloween to maximize the number of his victims. He drove south on the bike path, which runs along the Hudson River, plowing into bicyclists and sending riders into the air and crushing others on the ground.

The eight fatalities included six tourists, five from Argentina and one from Belgium. The two other victims were a 23-year-old software engineer from Manhattan and a 32-year-old financial worker from New Jersey.

During the penalty phase of Mr. Saipov’s trial, which began on Feb. 13, the jury heard emotional testimony from survivors of the attack and from relatives of people who were killed about the devastating impact the loss of their loved ones had on their lives.

Mr. Saipov’s lawyers presented testimony from Mr. Saipov’s parents and other family members in an attempt to humanize him before the jury.

Mr. Saipov did not testify in either phase of his trial.

In the government’s summation Tuesday, Ms. Houle presented facts and circumstances — so-called aggravating factors — that she said justified death.

She said, for example, that Mr. Saipov had committed his attack in support of ISIS, a terrorist organization. “Committing murder is always horrific,” she said, “but committing murder for a terrorist organization that has as a core purpose killing and terrorizing Americans” made him more culpable, she said, and more deserving of the death sentence.

She also noted that Mr. Saipov had decided against attacking a location like Times Square, where traffic and congestion would make it too difficult to reach his “maximum kill count.” Instead, he had used a bike path, a place enjoyed by children and other New Yorkers as well as tourists.

“The defendant exploited and attacked that sense of security and joy, leading to terror and devastation, and that is exactly what he wanted,” Ms. Houle said.

She also noted that Mr. Saipov had engaged in substantial planning and numerous killings and was likely to commit future violence in prison, and that he exhibited no remorse.

Ms. Houle displayed graphic images of each of the deceased victims, many of which showed their mangled and bloody bodies, some lying on top of bushes and others on the pavement of the path.

“It is brutal to look at these photographs, but it is important because that brutality is exactly what the defendant intended,” Ms. Houle said.

Mr. Patton told jurors that the defense was asking for a life sentence “not because Mr. Saipov didn’t cause extraordinary harm — he did.”

He said a decision for life also had nothing to do with sympathy, but “everything to do with our collective values and our shared sense of humanity.”

“Nothing we do can undo what Mr. Saipov did,” Mr. Patton said.

Mr. Patton, the city’s federal public defender, described mitigating factors for the jury to weigh, including how “secure and severe” Mr. Saipov’s life would be in prison, the fact he was subjected to manipulative recruiting by ISIS and that he is still loved by his family.

Mr. Patton displayed photographs of the prison where Mr. Saipov would serve a life sentence, the Administrative Maximum Facility in Florence, Colo., which is one of the country’s most highly restrictive. He would spend the rest of his life in a small cell with a concrete bed, desk and stool, with a five-inch window that looks out onto a concrete courtyard.

The defense also presented photos of Mr. Saipov as a young boy in Uzbekistan, including one with his sisters and mother, Mukaddas Saipova, who testified in the trial. Mr. Patton reminded the jury of testimony from one sister about how Mr. Saipov would dress up as Santa Claus during the holidays.

Mr. Patton said that at some point, Mr. Saipov became “consumed by ISIS propaganda,” adding that three years before the attack, he began watching the group’s violent martyrdom videos on his phone and at some point received an invitation to a join a Telegram chat group.

“But if you are going to decide between life and death, surely it matters that he spent a lifetime, before going down this God-awful hole of material, loving his family, getting a job, following in his father’s footsteps, coming to America, working hard, all the things you would hope for someone,” Mr. Patton said.

On Wednesday morning, the judge, Vernon S. Broderick, is expected to instruct the jurors on the law, and then the jury will retire to begin its deliberations.