Authorities said a man threw Molotov cocktails and used a "makeshift flamethrower" at a peaceful march for Israeli hostages in Boulder, Colorado, on Sunday, and the incident has shaken Chicago area chapters of the group that organized the march.

The FBI called the attack a "targeted act of violence."

The suspect was identified as 45-year-old Mohamed Sabry Soliman, FBI Special Agent in Charge Mike Michalek said Sunday evening. Soliman was allegedly heard yelling "free Palestine" during the attack, according to Michalek.

Boulder police initially said eight people were injured; they raised the total to 12 on Monday afternoon after officials said four more people with less serious injuries came forward.  

A walk to remember the Israeli hostages who remain in Gaza was taking place in Boulder's downtown at the time of the attack. Two sources said witnesses told investigators the suspect also allegedly yelled "End Zionist!" during the attack.

Among those injured were four women and four men ranging in age from 52 to 88, police said. One was seriously injured, with Boulder Police Chief Stephen Redfearn saying it would be "safe to say" that person was in critical condition.

Soliman has been charged with multiple felony counts, including attempted murder, and a federal hate crimes charge.

"Mr. Soliman stated that he had been planning this attack for a year, and he acted because he hated what he called his Zionist group," said J. Bishop Grewell, Acting U.S. Attorney for the District of Colorado.

Police say they also found 14 unused Molotov cocktails with Soliman. Soliman reportedly found information to make Molotov cocktails on YouTube, and the flamethrower he is accused of using was made from gardening equipment.

Multiple sources told CBS News that Soliman is an Egyptian national who arrived in the U.S. in 2022 on a non-immigrant visa that has since expired. Investigators say Soliman had previously tried to buy a gun before the attack, but could not do so because he is not a legal citizen.

Speaking with CBS News Chicago on Monday from New York, Run For Their Lives global coordinator Shira Weiss says the Boulder chapter has met regularly for more than a year.

"This is actually the first violent incident that any of our groups have ever encountered," said Weiss.

Run For Their LIves also has several chapters in the Chicago area. The website for the organization gives information for two groups in the city — in Lakeview and Lincoln Park/DePaul, and six suburban chapters — in Buffalo Grove, Deerfield, Hazel Crest, Highland Park, Oak Park, and Skokie.

Some participants in the Chicago area chapters have long been worried about their safety.

"Safety has always been our top priority," Weiss said. "We've always told the group leaders that you know our mission is apolitical. It's, you know, not protest. It's not a demonstration. It's literally a walk to raise awareness for the hostages."

Video on social media shows a Chicago meetup happened just hours before the Boulder attack. Local organizers said they typically meet the same place, same time each week, their regularity and visibility bringing safety concerns.

"We don't post the locations on our website," said Weiss. "You do have to join a Whatsapp group to get that information.

One suburban leader of Run For Their Lives said they have repeatedly asked for protection from their local police department, and security is even more concerning now.

Illinois Governor JB Pritzker posted the following message to social media after the attack in Colorado:

"Horrified by today's terror attack in Colorado. Antisemitism has no place in our nation and we must continue to unite together against such hatred. Our hearts are with the victims and their loved ones."