The gunman who killed 11 worshipers in a Pittsburgh synagogue in October 2018 was found guilty on Friday of dozens of federal hate crimes and civil rights offenses, closing the first stage of a trial that may ultimately end in a death sentence.

After five hours of deliberations over two days, the jury found the gunman, Robert Bowers, guilty of 63 federal charges, including 11 counts of obstructing the free exercise of religious beliefs resulting in death.

Now the trial will turn to the question of punishment. The jury will hear arguments about whether Mr. Bowers, 50, is eligible to be sentenced to death for these crimes. If the jurors decide that he is, they will then decide whether the death sentence should be imposed. These next two phases of the trial are expected to last around a month and a half.

The outcome of this first phase was in little doubt. Mr. Bowers’s defense team did not call a single witness. His lawyers have not disputed that he planned and carried out the massacre, which is considered to be the deadliest antisemitic attack in U.S. history.

The primary objective for the defense, as conveyed in court filings leading up to trial, has been to avoid a death sentence. Lawyers for Mr. Bowers made offers to plead guilty to all counts in exchange for life in prison without the possibility of parole, but the Justice Department rejected those offers.

In the first phase of the trial, defense lawyers raised questions about Mr. Bowers’s motives and intent, and whether the evidence presented by the government satisfied the elements of some of the federal charges. They also suggested that his state of mind may be a key part of their arguments in the penalty phase.

“How and why did this man, who up until Oct. 27, 2018, had lived a solitary and law-abiding life, wreak the havoc and destruction that he did?” Elisa Long, a federal public defender who is representing Mr. Bowers, said in her closing argument.

The verdict on Friday came after three weeks of testimony, including chilling accounts of worshipers who survived the mass shooting huddling in closets or lying near death in a hallway, as Mr. Bowers stalked the Tree of Life synagogue with three handguns and a semiautomatic rifle. Three congregations were meeting for services in the building that morning: Tree of Life, New Light and Dor Hadash. Members of each were among the people killed or wounded by Mr. Bowers.

“We were filled with terror,” said Andrea Wedner, who recounted lying on the floor of a chapel, her right arm shattered by bullets, trying to comfort her dying 97-year-old mother. “It’s indescribable.”

The 60 witnesses called by the prosecution included police officers who rushed into the synagogue, some of whom were injured in shootouts with Mr. Bowers; businessmen who sold Mr. Bowers his gun holsters; the chief executive of Gab.com, the social media site where Mr. Bowers posted prolifically about his hatred of Jews and immigrants; and the president of a Jewish organization that helps resettle refugees — a mission that Mr. Bowers said spurred him to attack the synagogue.

The testimony was often harrowing. Recordings of 911 calls were played, filling the courtroom with the sounds of people being shot to death. Prosecutors showed graphic photographs of the aftermath. Pathologists described autopsies in clinical detail: a bullet wound so severe that they “could see inside the space where the brain sits”; a woman killed by a gunshot that “more or less cut the heart in two.”

Experts testified about the barrage of antisemitic posts that Mr. Bowers made on Gab.com, celebrating the Holocaust and calling for the eradication of Jews.

“The message that the defendant chose to tell the world about himself was clear and unambiguous: He is filled with hatred for Jews,” Mary Hahn, a federal prosecutor, said in her closing argument.

Other witnesses were called upon to describe tenets of the Jewish faith, and to explain how the congregations had changed after the attack.

“We don’t have the same attendance,” Stephen Weiss, the longtime ritual director for Tree of Life, said. It has been more difficult to reach the required minyan, or quorum, of 10 people in order to recite certain prayers. Those members who could always be counted on to show up on time for services, Mr. Weiss said: “They were killed.”

Throughout much of this testimony the defense team sat quietly, asking a few questions of some of the prosecution’s expert witnesses but largely letting the proceedings unfold on the government’s terms. The defense lawyers indicated at several points that their case would come mostly in the subsequent phases of the trial, when the jury would make decisions about the death penalty.