"George Zimmerman has informed United Gun Group that he currently is in the process of vetting several offers and verifying funds," the online marketplace tweeted.
Reached for comment, Zimmerman directed CNN to his website. There, in a statement addressed to "fellow patriots," Zimmerman said the auction was successful and had raised funds for worthy causes. He thanked the United Gun Group and its owner for having the "moral fortitude in hosting my firearm auction."
"The winning bidder will ultimately decide if they want their information to be maintained in confidentiality and they are assured that I will withhold their identity from all media and private parties," he wrote in a statement, saying the auction was officially closed and the winning bidder would be notified immediately.
Whether the $138,900 bid was the winner is unclear, as there were two auctions running simultaneously, one for pre-qualified bidders and one for the general public, according to United Gun Group.
Someone bidding as John Smith offered $138,900, beating out at the 11th hour a David Thorne, who had bid several times, sometimes outbidding himself.
United Gun Group initially declined to host the auction after another gun auction site, Gunbroker, said it wanted "no part in the listing on our website or in any of the publicity it is receiving."
At first, United Gun Group said, "Our mission is to esteem the 2nd Amendment and provide a safe and secure platform for firearms enthusiasts and law-abiding citizens; our association with Mr. Zimmerman does not help us achieve that objective."
Later, it recanted, and Zimmerman put what he called "a piece of American history" on the site with a starting bid of $100,000 and a "buy it now" price of $500,000.
"I am honored and humbled to announce the sale of an American firearm icon," the website said. "The firearm for sale is the firearm that was used to defend my life and end the brutal attack from Trayvon Martin on 2/26/2012."
Zimmerman took shots at GunBroker in his post-auction statement, calling the site GunJoker and "Nazi loving liberal liars."
Gun's dubious history
The 32-year-old former neighborhood watch volunteer -- seen by some as a national pariah and by others as a hero -- announced plans to sell the Kel-Tec PF-9 weapon last week. The 9mm pistol carries a suggested price of $356.36 on the manufacturer's website.
In February 2012, Zimmerman called police to report what he described as a suspicious person -- Martin, an unarmed African-American teen
-- walking in his neighborhood, then disregarded police instructions not to confront him.
He said the teen attacked him and he shot in self-defense.
A jury acquitted him in 2013.
Martin's family declined to comment last week, saying it was working to end gun violence through the Trayvon Martin Foundation.
"This election season, we are laser focused on furthering that mission," they said in a statement. "As such, the foundation has no comment on the actions of that person."
Family attorney Benjamin Crump was more willing to share his thoughts.
"It's like he is shooting and killing Trayvon all over again four years later with this attempt to auction off this gun like it's some kind of trophy," Crump said. "I mean, it's offensive, it's outrageous and it's insulting."