The pistol used to kill unarmed black teenager Trayvon Martin appears to have been removed from an online auction.
George Zimmerman, who shot and killed the 17-year-old, had planned to auction it on the website Gun Broker.
The bidding was due to begin on Thursday, with the first bid starting at $5,000 (£3,450).
Mr Zimmerman, 32, a neighbourhood watchman, was cleared over the death of the teenager in February 2012 after saying he acted in self-defence.
In an online posting to announce the auction, Mr Zimmerman said that he would use the profits to “fight” the Black Lives Matter movement and oppose Democrat Hillary’s Clinton’s presidential campaign.
A lawyer for the Martin family told the Washington Post that “it is insulting to this family that he would decide that he would sell the gun that he killed their child with”.
“Think about what that means: This is a gun that took a child’s life and now he wants to make money off of it.”
On the auction site, Mr Zimmerman refers to the gun as an “American icon”, and says it was recently returned to him by the US Department of Justice.
He claimed that the Smithsonian museums had expressed interest in buying the 9 mm handgun, but Smithsonian officials denied that in a statement.
Speaking to a Florida radio station, Mr Zimmerman had defended the auction saying “I’m a free American, and I can do what I’d like with my possessions.”
Analysis – Nick Bryant, BBC North America correspondent
Few cases in recent years have been more racially sensitive or led to such an anguished national conversation as the killing of Trayvon Martin. It sparked demonstrations around the country, prompted President Obama to remark that if he had a son, he’d have looked like the black teenager and brought about the first use on social media of the hashtag “Black Lives Matter.”
So the decision of the former neighbourhood watchman, George Zimmerman to put the gun he used up for auction not only seems extraordinary but also cruel and callous – especially since he refers to the weapon on the online site as an “American icon.”
This is not the first time that Zimmerman has sought to cash in on his notoriety. His first painting of an American flag, emblazoned with the words “God One Nation with Liberty and Justice For All,” sold on eBay for the staggering sum of $100,000. But it did not impress critics, who called it “primitive” and “appalling.”
Harsher language will no doubt be used to describe the sale of the pistol that killed Trayvon Martin.
Congressman Hakeem Jeffries said on Thursday that “Trayvon Martin’s cold-blooded killer should be in prison. Instead, he is trying to profit from the stunning miscarriage of justice.”
Florida police did not arrest Mr Zimmerman for six weeks after the shooting in Sanford, Florida, provoking mass rallies in Florida and throughout the US.
Police justified their decision not to detain him by citing the state’s controversial “stand your ground” law, which allows a citizen to use lethal force if he or she feels in imminent danger. Police initially said the law prevented them from bringing charges.
Profiles: Trayvon Martin and George Zimmerman
Mr Zimmerman’s defence said Trayvon Martin had punched their client, slammed his head into the pavement and reached for Mr Zimmerman’s gun. Prosecutors accused Mr Zimmerman of telling a number of lies.
The case led to protests in several cities in the US and to the birth of the Black Lives Matter movement.
Mr Zimmerman’s name has been in news headlines several times since his closely watched trial.
Twice, assault charges against his girlfriend were dropped.