The online auction for the pistol George Zimmerman used to shoot and kill unarmed American teenager Trayvon Martin in 2012 was up to US$65 million on Friday, though the action has been trolled by buyers with usernames like "Racist McShootFace".
Zimmerman drew wide criticism on Thursday after offering to sell the Kel-Tec PF9 9mm handgun, which the former neighbourhood watch volunteer described in the auction listing as "an American Firearm Icon".
Zimmerman said the weapon was used to defend his life and "end the brutal attack" from Martin.
Martin's death in Florida sparked nationwide civil rights protests after Zimmerman was acquitted of second-degree murder and manslaughter charges in the case.
Martin's family has said the 17-year-old was walking home after buying a drink and candy from a local store.
On Friday morning, bidders in the auction on the United Gun Group's website included "shaniqua bonifa" and "Tamir Rice," the same name as the 12-year-old black boy shot dead by a white police officer in Cleveland in 2014, Reuters reports.
Though it now appears many of those bids have been deleted, as had comments about it.
The auction began on Thursday afternoon after the first site on which Zimmerman attempted to sell the gun rejected the listing. That site, GunBroker.com, said in a statement that it wanted no part in the auction or the attendant publicity.
A listing for the gun then appeared on UnitedGunGroup.com, with a starting price of US$5000 (NZ$7400).
On its Facebook page, the United Gun Group said: "United Gun Group's stance is that as long as Mr Zimmerman ... is obeying the letter of the law, his personal firearm sale will be permitted on our network," the group said on its Facebook page.
In the listing, Zimmerman said he would use money from the sale to counter violence against law enforcement officers by Black Lives Matter, a movement that grew out of Martin's shooting. Proceeds would also go toward fighting Democratic presidential hopeful Hillary Clinton's "anti-firearm rhetoric".
A lawyer for Martin's family called the auction offensive but said it would not distract the family from their work advocating against gun violence.