As New York City prosecutors worked Thursday to bring murder charges against Luigi Mangione in brazen fashion murder of UnitedHealthcare CEO Brian Thompsonthe suspect’s supporters are donating tens of thousands of dollars to a defense fund set up for him, leaving law enforcement officials worried that Mangione will be turned into a martyr.

Several online advocacy funds have been set up for Mangione by anonymous people, including one on the crowdfunding site GiveSendGo that, as of Thursday afternoon, had raised more than $50,000.

The GiveSendGo defense fund for Mangione, 26, was created by an anonymous group calling itself the “December 4th Legal Committee,” apparently in reference to the day Mangione allegedly ambushed and shot Thompson in Midtown Manhattan while the executive was heading towards his seat. company shareholders conference at the Hilton Hotel in New York.

“We are not here to celebrate violence, but we believe in the constitutional right to fair legal representation,” the anonymous group said in a statement.

The crowdfunding campaign attracted donations from more than 1,500 anonymous donors across the country, many of whom left messages of support for Mangione, including one person who called themselves a “frustrated citizen” and thanked Mangione for having “awakened consciousness and reflection in this sleeping nation. “.

The GiveSendGo fund for Mangione appeared to be briefly removed before being reinstated Thursday. GiveSendGo did not immediately respond to ABC News’ requests for comment.

Other crowdfunding sites such as GoFundMe have also removed campaigns seeking donations for Mangione’s defense.

“GoFundMe’s terms of service prohibit fundraising for the legal defense of violent crimes,” the crowdfunding site said in a statement. “Fundraisers have been removed from our platform and all donors have been refunded.”

Amazon and Etsy have removed products featuring Mangione from their websites, including T-shirts and tote bags emblazoned with “Free Luigi” and the phrase “Deny, Defend, Depose,” words that the police, were engraved in the shell casings discovered at the scene of the Thompson attack. homicide.

“To celebrate this conduct is repugnant to me. It’s deeply disturbing,” Manhattan District Attorney Alvin Bragg told ABC News senior investigative reporter Aaron Katersky in an interview Wednesday evening. “And what I would say to members of the public, to people who are, as you described, celebrating this and perhaps considering further actions, that we will be vigilant and we will hold people accountable. We are ready .”

Prosecutors with the Manhattan District Attorney’s Office have begun presenting evidence to a grand jury as they try to obtain an indictment against Mangione, sources told ABC News on Thursday.

Mangione’s attorney, Thomas Dickey of Altoona, Pa., where Mangione was arrested Monday after a five-day manhunt, said his client is presumed innocent and will plead not guilty to the charges. against him. Mangione is contesting his extradition to New York.

Asked about people contributing to Mangione’s defense funds, Dickey said: “People are entitled to their opinions and, like I said, if you’re an American and you believe in the American criminal justice system, you must assume it. to be innocent and none of us would want anything else if it were us in their place. So, I’m glad he had some support.

But law enforcement officials have expressed concern that Mangione is being turned into a martyr. This week, someone posted “wanted posters” outside the New York Stock Exchange naming other executives.

A bulletin released Wednesday by the Delaware Valley Intelligence Center, a multi-agency intelligence-sharing network based in Philadelphia, included a photo of a banner hanging from an overpass reading “Deny, Defend, Depose.”

“Many social media users have openly advocated for continued CEO assassinations, with some aiming to sow fear by posting ‘blacklists,'” read the bulletin, obtained by ABC News.

Meanwhile, New York Police investigators continue to build a murder case against Mangione, who is being held in Pennsylvania on charges stemming from his arrest there, including illegal possession of a phantom gun and fraudulent identification. Mangione has pleaded not guilty to the charges in Pennsylvania.

On Wednesday, New York Police Commissioner Jessica Tisch said the three shell casings recovered at the scene of Thompson’s shooting matched the gun found in Mangione’s possession when he was arrested. She also confirmed that Mangione’s fingerprints were found on a water bottle and granola bar wrapper found near the crime scene.