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Mr Cull said he stopped the sale at Hayward's Auction House yesterday to ensure artefacts were not released on the open market.
An investigation would reveal their authenticity, he said.
If they were found to be authentic leg irons, the Dunedin City Council would consider buying them as they would be significant to the Parihaka community in Taranaki, ''which is why I stepped in to secure these''.
Dunedin man Steve McCormack, who is trying to sell the item, said he and his late brother removed the ''leg irons'' from a cave in Portobello Rd in the 1970s.
The cave is in an area where Maori prisoners from Taranaki were forced to labour between 1869 and 1871.
Mr Cull said Mr McCormack would be interviewed as part of the investigation.
Toitu Otago Settlers Museum acting director Jennifer Evans said it was working to authenticate the shackles. The release date of investigation findings was not yet known, she said.
A Parihaka spokesman, Ruakere Hond, of New Plymouth, said the auction of the ''stolen'' shackles was ''obscene and morally repugnant''.
An auction would be an ''insult'' to the men imprisoned illegally in caves in Dunedin.
''The people of Parihaka, the descendants of the prisoners incarcerated with hard labour for their beliefs, want to have it known that this sale is reprehensible,'' he said. Mr McCormack should not benefit financially from the sale of the shackles, Mr Hond said.
However, Mr McCormack said he would still sell the irons.
He said Mr Hond should be appreciative he had preserved the leg irons and if the Parihaka people wanted the item, they could place a bid.
''I'm not giving them away.''
However, Dunedin historian Bill Dacker said the shackles, which were pictured in the Otago Daily Times on Tuesday, were not leg irons but horse hobbles.
The cave where Mr McCormack found the shackles was big enough to house a horse and had no history of housing prisoners, Mr Dacker said.
Mr McCormack could have wrongly mistaken the cave for a prison when he entered it in the early 1970s, Mr Dacker said.
''He could have seen places for tethering horses.''