Testimony concluded on Monday in the federal trial of the man who killed 11 worshipers in a Pittsburgh synagogue, as the defense and prosecution laid out, in their closing arguments, the conflict at the heart of the case: whether the man who carried out the massacre was driven by a cold, calculated hatred or by a diseased mind.

After nearly three months and more than 100 witnesses, all that remains in the trial is for the jury to decide whether the defendant, Robert Bowers, should spend the rest of his life in prison or be condemned to death for the October 2018 attack.

Deliberations are expected to begin on Tuesday morning.

The facts of the crime, considered the deadliest antisemitic attack in the country’s history, have never been in dispute. In June, after weeks of harrowing testimony from survivors, Mr. Bowers was convicted on 63 counts, including hate crimes that carry a potential death sentence. In mid-July, the jury determined he was eligible for the death penalty. Since then, the trial has focused on whether that should be his sentence.

In urging the jurors to vote for a death sentence, Eric Olshan, one of the prosecutors, outlined the nine aggravating factors that the jurors will consider, including the extensive planning, the setting in a house of worship and the lack of any apparent remorse.

One by one, Mr. Olshan, the U.S. attorney for Western District of Pennsylvania, gave brief sketches of those who were killed — Joyce Fienberg, 75; Richard Gottfried, 65; Rose Mallinger, 97; Daniel Stein, 71; Melvin Wax, 87; Irving Younger, 69; Dr. Jerry Rabinowitz, 66; the couple Bernice, 84, and Sylvan Simon, 86; and the brothers Cecil, 59, and David Rosenthal, 54 — showing old family photos and recounting the effect of their deaths on those around them.

He then went through the list again, this time showing photos of each victim as he or she was found in the pews or on the floors of the synagogue, many of them lying in pools of blood. He described in detail what bullets had done to them and the bodies of the six other people who were badly injured.

That degree of loss was immeasurable, he said. “But you still must take the impact of all of that loss, for each of the 11, and put it on the scale.”

Mr. Olshan highlighted remarks that Mr. Bowers made to psychiatrists who had examined him — mostly witnesses called by the defense — in which he regretted only that he had not killed more Jewish people. He dismissed the defense’s arguments that Mr. Bowers was incapable of feeling remorse because of his schizophrenia, a diagnosis made by several psychiatrists but one that the prosecution has disputed.

In her closing argument, Judy Clarke, a lawyer for Mr. Bowers, argued that deciding whether to put someone to death required going beyond the facts of the crime to the circumstances of the defendant’s life. “You can’t stop with the crime and the harm that it caused,” she said. “Those of you that have to make an extraordinary decision about the life of another fellow citizen can’t stop there.”

She recounted the weeks of testimony about Mr. Bowers’s upbringing, depicting a family plagued by serious mental illness, including depression and schizophrenia. Mr. Bowers’s life was chaotic and troubled from the time he was an infant, Ms. Clarke said, showing the jury a series of images from official reports recording his repeated suicide attempts and commitments to mental health facilities.

Ms. Clarke argued that there were times when Mr. Bowers tried to overcome his challenges, finding work or getting limited medical attention. But she said his mental health spiraled sharply in the years leading up to the attack when, in rapid succession, he lost his grandfather, his house and his only close friend.

“It is then that he succumbed to his mental illness, to his delusional beliefs, and brought us where we are today,” she said.

Describing those pivotal few years, she focused on the testimony of Dr. George Corvin, a forensic psychiatrist who testified last week and had interviewed Mr. Bowers in prison for nearly 40 hours. Mr. Bowers had become obsessed with the idea of an impending apocalypse, Dr. Corvin said, and had come to believe that Satan was using Jewish people to bring about a race war between whites and nonwhites. Mr. Bowers believed that it was his divine mission to fight back, and that’s what he thought he was doing when he carried out his attack, Dr. Corvin concluded.

“He was mentally ill as a child, he was mentally ill as an adult, and ultimately he descended into serious mental illness and committed these horrible crimes and what a tragedy is that,” Ms. Clarke said. “But is that who we kill?”