The mayor's office learned before a news conference announcing the plan Tuesday that the guns already collected couldn't be used in the plaques, McGinn spokesman Aaron Pickus said Thursday.
Nevertheless, as first reported by KIRO-FM, the mayor left the impression at the news conference that they would be.
"We were inspired by the idea that we could take these weapons that were recovered, 750 at the first gun buy back, and do something meaningful with them - something of symbolic importance to our city, particularly after all the incidents of gun violence we have seen in this city over the years," McGinn said.
He went on to explain that the "Weapons to Words" program would take succinct quotations from schoolchildren about gun violence, and engrave them "on plaques using steel that has been upcycled from the guns recovered in our gun buyback program."
The mayor's news release later Tuesday explained it this way: "The plaques, made from upcycled steel that includes the weapons we recovered, will be placed in Seattle parks."
Sgt. Sean Whitcomb, a spokesman for Seattle police, said Thursday that the department had the guns melted down due to "a miscommunication."
Asked why the mayor hadn't been more forthcoming, Pickus said the city has been planning to do more gun buybacks, and would use those guns for the peace plaques. He said the mayor was prepared to give specific details on what happened with the guns collected in January if any reporters asked.
Asked why reporters might have suspected that the guns had already been recycled, Pickus said, "That's a great question."
He went on to suggest that which gun buyback the guns for the plaques come from isn't relevant to the larger point of the anti-violence message.
"It was a detail that wouldn't impact this outreach effort," Pickus said. "It is what it is."
The buyback program was announced a month after last December's elementary school massacre in Newtown, Conn., by city leaders sick of hearing about gun violence. Private sponsors, including Amazon.com, contributed tens of thousands of dollars so that people could anonymously turn in their weapons for shopping cards worth up to $200. The plan all along was to use the guns collected in some kind of public art project.
The "Weapons to Words" program is supported by Schnitzer Steel and the studio of famed glass artist Dale Chihuly, which is helping to design the plaques.