Eight people were injured in the attack on Sunday in the U.S. city of Boulder, who are running for the release of Hamas and other Palestinian armed groups in Gaza.
Police arrested a man who allegedly applied burning devices to people. The FBI said it was investigating the attack as a "terrorist act."
In social media posts, Israeli Foreign Minister Gideon Saar described the attack as an anti-Semitic act.
Here is what we know so far:
According to an official press release from the Boulder Police Department, a group of people are participating in a “regularly scheduled, weekly peace event” aimed at inspiring support for those who released their captives during the Gaza attack. Police were called at 1:36 p.m. (10:36 GMT).
The attacker used a temporary flamethrower when witnesses blew the burner device (designed to fire) at the party.
Witness videos circulating on social media showed a shirtless man who seemed to hold two glass bottles, looking like a Molotov cocktail.
Molotov cocktails are a very simple burning weapon. It includes a bottle filled with a flammable liquid covered with a wick that ignites before the bottle is thrown to the target.
They were named after the Soviet Foreign Minister Vyacheslav Molotov during World War II. In 1939, the Soviet Union invaded Finland and the country suffered heavy bombing. Molotov insisted that the Soviet Union had no bombs, only food packages.
In response, the Finns threw handmade explosives at Soviet tanks, sarcastically dubbing them as "Molotov cocktails."
The attack took place at the Outdoor Pearl Street Mall, a pedestrian shopping center in downtown Boulder that stretched four blocks. It is home to retail stores, art galleries and restaurants. The shopping mall is a two-minute drive away, 1.1 km (0.7 miles) from the University of Colorado-Boulder.
Colorado Attorney General Phil Weiser issued a statement Sunday saying the attack was a "group against weekly meetings at the Pearl Street Mall in Boulder, calling for the release of hostages in Gaza".
The Anti-Defamation League (ADL), a nonprofit that works to combat anti-Semitism -- a coalition accused of defending billionaire Elon Musk in January defending a tribute tribute at an opening rally for U.S. President Donald Trump -- released a statement saying the incident was part of an international campaign.
The campaign involves weekly gatherings around the world, with members of Jewish community running and walking with captives captured by Hamas and other Palestinian groups as they attack Israel on October 7, 2023.
Campaigns are held in 230 locations in 24 countries, including Brazil, Canada, India, New Zealand, South Africa and Spain. Groups from several states in the United States participated in the event, with Colorado having two locations: one in Boulder and the other in Washington Park in Denver.
Armed Palestinian groups seized about 251 prisoners from Israel on October 7. When some prisoners were sent back in exchange for Palestinian prisoners, or were rescued, others died in captivity. About 59 prisoners are believed to be imprisoned, and 35 of them are believed to be dead in Israel.
According to the Gaza Government Media Office, Israeli military bombing and other attacks have killed more than 61,700 Palestinians in the Gaza Strip since October 7.
According to a Boulder Police press release, the suspect in the boulder attack has been identified as Mohamed Sabry Soliman, a 45-year-old man in El Paso County.
Soliman was also injured in the attack, although the nature of his injury is not yet known.
Soriman was medically evaluated at the hospital and was booked at the Boulder County Jail for multiple charges, the release said. This version does not specify what these fees are.
According to the press release, Soriman shouted "Free Palestine" in the attack.
White House Deputy Chief of Staff Stephen Miller claimed in an article on X that the boulder attack was carried out by "illegal foreigners."
Miller did not name Soliman, saying the suspect was too high a tourist visa granted to him by former U.S. President Joe Biden's administration. "In response, the Biden administration gave him a work permit. Suicide migration must be completely reversed," Miller wrote.
Al Jazeera cannot independently verify Soliman's immigration status in the United States.
Law enforcement officers said eight people were injured. These included four women between the ages of 52 and 88 and four men.
The victim was taken to a hospital in the Denver metro area.
The Boulder Police Department called the FBI within minutes of the attack, the press release said. The FBI has investigated it as a terrorist attack.
"Based on early information, evidence and witness statements, this terrorist act is being investigated as an ideologically motivated act of violence," FBI Deputy Director Dan Bongino wrote in an X post. "We will talk clearly about these events when facts guarantee facts."
FBI Director Kash Patel also wrote in an X post that his team is investigating "targeted terrorist attacks" while FBI agents and law enforcement are already on the scene.
Homeland Security Secretary Kristi Noem wrote in an X post that the department is working on the situation with "inter-agency partners" including the FBI.
According to the latest news from the Boulder Police Department at 05:53 GMT, besides a block on Pearl Street, “should be reopened in the next few hours.”
"We will continue to ensure that justice is sought quickly, support victims and take precautions to protect everyone's safety," said Mark Michalek, special agent for the FBI Denver (FBI) Denver (FBI) in Bolder Police News Reparse Repares.
Boulder Police Chief Stephen Redfearn admitted that many residents were afraid and had questions about the attack. "Boulder has recovered from violence before and we will recover again. I urge this community to come together. It's not the time to split," he was quoted in the same press release.
"The horrible anti-Semitic terrorist attacks against Jews in Boulder, Colorado were shocked. It was purely anti-Semiticism, driven by blood slander spreading in the media," Israeli Foreign Secretary Saar wrote on Monday X. He did not elaborate on what he meant.
"Tonight, a peaceful demonstration was directed against evil anti-Semitic terror. Again, Jews are once again free from repeated violence and terrorism," wrote Chuck Schumer, a Democratic leader of the U.S. Senate, wrote on X.
"We pray for the victims of the targeted terrorist attack in Boulder this afternoon," U.S. Secretary of State Marco Rubio wrote on Sunday X.
We unite and pray for the victims of the targeted terrorist attacks in Boulder this afternoon.
Horror has no place in our great country.
- Secretary Marco Rubio (@secrubio) June 1, 2025
Many Democrats issued online statements denouncing the attack and described it as anti-Semitism.
Less than two weeks after the terrifying anti-Semitic attacks at the Jewish Museum in Washington, D.C., and after two years of ruthless attacks across the country, the Jewish community once again undermined the Jewish community with pain and heartbreak.
Tonight, a peaceful demonstration...
— Chuck Schumer (@senschumer) June 2, 2025
"My thoughts are with the victims, their families and Jewish communities, and seem to be targeted again. We all have a duty to stop these anti-Semitic behaviors," wrote on X.
Another terrifying attack in Boulder, Colorado this time. My idea is to be with the victims, their families and the Jewish community, and it seems to be the target of hatred again. We all have a responsibility to stop these anti-Semitism.
— Elizabeth Warren (@senwarren) June 2, 2025
Hakeem Jeffries, a Democrat, issued a statement on X: “Our wholehearted prayer and the prayers of all our Jewish siblings affected by this incredible act of terror, and we thank the law enforcement for the quick response. Anti-Semitism has no place in our country or around the world.
My statement about the anti-Semitic attacks in Boulder, Colorado. pic.twitter.com/eupdnl9m6k
- Hakeem Jeffries (@repjeffries) June 1, 2025
On May 22, a man named Elias Rodriguez was charged in Washington, D.C. He was charged with murdering a foreign official, causing death with a gun, and releasing the gun on a crime of violence.