John BranchAlexandra E. Petri and Mark Walker Six people were hospitalized with “burns and other injuries” sustained in downtown Boulder, Colo., on Sunday afternoon, authorities said, after an attack on a group raising awareness about Israeli hostages being held in Gaza. The victims ranged in age from 67 to 88 and their injuries were anywhere from serious to minor, authorities said. Two were airlifted to a burn unit at a hospital in the Denver area, officials said. The suspect was identified as Mohamed Sabry Soliman, 45, by Mark Michalek, the F.B.I. special agent in charge of the agency’s Denver field office. He said that witnesses reported that the suspect had used a “makeshift flamethrower” and thrown an incendiary device into the crowd, adding that “the suspect was heard to yell, ‘Free Palestine’ during the attack.” Here’s what to know: Calls for help: Calls about an emergency on the Pearl Street pedestrian mall near Boulder’s county courthouse came in starting at 1:26 p.m. local time, the chief said in a news conference. Initial reports mentioned a man with a weapon and said people were being set on fire. Chief Redfearn said investigators were not entirely certain of what happened, but the report was “fairly consistent with the injuries that we found on scene.” Suspect arrested: The suspect, Mr. Soliman, was taken into custody after witnesses pointed him out, the chief said. Videos on social media showed a man, shirtless and holding two bottles, shouting while bystanders helped injured people nearby. Patches of grass in front of the courthouse were on fire. A peaceful gathering: The victims were participating in Run for Their Lives, a weekly event that has brought attention to the Israeli hostages being held in Gaza since the Thanksgiving after the Oct. 7, 2023, terrorist attacks in Israel. “Our walk has been nothing ever but peaceful, and this was a blatant act of antisemitism on the streets of Boulder,” said Rachel Amaru, a leader of the group. “Appears to be a hate crime”: The attorney general of Colorado, Phil Weiser, a Democrat, said in a statement that “this attack appears to be a hate crime given the group that was targeted.” He added, “People may have differing views about world events and the Israeli-Hamas conflict, but violence is never the answer to settling differences.” Mark Walker Every Sunday at 1 p.m. in Boulder, Colo., the walkers take their places. They have done so since a few weeks after the Oct. 7, 2023, Hamas-led attack on Israel. They begin at Pearl and Seventh Streets and walk toward the courthouse, along a pedestrian mall. Lisa Effress, 55, who has lived in Boulder for 17 years, has been there since the first walk. “Whenever I’m in town,” she said, “I try to be there.” The ritual is simple: walk, speak the names of those still held hostage, sometimes sing “Hatikvah,” the Israel national anthem, and bear witness. The numbers vary — 20, sometimes 100. People see the group, hear the songs, and fall into step. They wear red. It’s symbolic. It’s visible. Ms. Effress wasn’t walking this Sunday. She was across the street, having lunch with her daughter. But lunch got cut short. She heard sirens. Police cars, ambulances. She checked the time and figured the group must be near the courthouse. She left lunch and ran over. “I knew immediately — I just knew,” she said. “I ran across the street, looking for everyone.” What she found felt surreal. Smoke. Discarded clothes used to extinguish flames. People dazed, half-undressed. Bags and backpacks left behind in panic. And then, she saw a friend who was a Holocaust survivor, being helped into an ambulance. “It looked like a war zone,” said Ms. Effress, a filmmaker and managing partner in a post-production company. “It was horrible.” On every walk, Ms. Effress said, she is vigilant. Alert to strange behavior, to tension in the air. “We are peaceful. We are not protesters,” she said. “But there are always people protesting us.” She added: “I have always taught my daughter: Be proud to be Jewish. Don’t be afraid. But in a time like this, it is crazy to think we will ever be walking again. It’s dangerous, it’s not safe for us.” She said that according to a Whatsapp chat for the walking group, the weekly walk has been canceled indefinitely. Alexandra E. Petri Chief Redfearn said that the authorities do not believe there is another suspect at large. “We are not going to say that with absolute certainty, because we are still conducting a lot of interviews,” he said, but officials have not been able to confirm an initial report regarding two suspects, he said. Alexandra E. Petri Chief Redfearn said at a news conference that four of the burn victims were taken to Boulder Community Hospital, while two were flown by helicopter to Denver. Alexandra E. Petri Michael Dougherty, the district attorney for Boulder County, said in a news conference that decisions would be made in the coming days about what charges to file and in which courts, to “hold the attacker fully accountable.” Alexandra E. Petri Mark D. Michalek, the F.B.I. special agent in charge, said the suspect in custody has been identified as Mohamed Sabry Soliman, 45, of Colorado Springs. Officials did not say whether he had been charged with anything or what charges he might face, responding only that the investigation was in its early stages. Alexandra E. Petri Chief Steve Redfearn of the Boulder Police said several downtown blocks have been closed off surrounding the county courthouse, where the attack took place. The area is still being search for explosive devices, he said. “We want to be reasonably sure, as best as we can,” that the area is as safe as possible, the chief said. Alexandra E. Petri Mark D. Michalek, the F.B.I. special agent in charge, said that witnesses told investigators that the suspect, who is in custody, used a “makeshift flamethrower” and threw an incendiary device into a crowd of people. He could be heard yelling “Free Palestine” during the attack, Michalek said at a news conference in Boulder. Alexandra E. Petri Officials said at a news conference in Boulder, Colo., that six people were injured in the attack on Sunday afternoon and taken to hospitals. They ranged in age from 67 to 88. Julian E. Barnes Tulsi Gabbard, the director of national intelligence, wrote in a social media post that the National Counterterrorism Center was working with the F.B.I. and local authorities “investigating the targeted terror attack” against Jewish community members in Boulder. The Counterterrorism Center helps coordinate and share intelligence about terrorist threats between the F.B.I. and intelligence agencies. John BranchAlexandra E. Petri and Mark Walker The attack on an event in Boulder, Colo., for Israeli hostages on Sunday afternoon was the latest on the Jewish community, following two others in recent weeks involving assailants who expressed anger over the war in Gaza. On May 21, two people were fatally shot outside the Capital Jewish Museum in Washington, D.C., after which the suspect shouted “Free Palestine.” In April, a man set fire to the residence of Gov. Josh Shapiro of Pennsylvania, who is Jewish. The suspect later said the fire was a response to Israeli attacks on Palestinians. “As the American Jewish community continues to reel from the horrific antisemitic murders in Washington, D.C., it is unfathomable that the Jewish community is facing another terror attack here in Boulder, on the eve of the holiday of Shavuot no less,” Colorado’s governor, Jared Polis, said in a statement. “Several individuals were brutally attacked while peacefully marching to draw attention to the plight of the hostages who have been held by Hamas terrorists in Gaza for 604 days. I condemn this vicious act of terrorism, and pray for the recovery of the victims.” Colorado’s attorney general, Phil Weiser, said in a statement that the attack “appears to be a hate crime given the group that was targeted.” “People may have differing views about world events and the Israeli-Hamas conflict, but violence is never the answer to settling differences,” he added. “Hate has no place in Colorado.”