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The leg irons were bought from the mayoral fund after research into their authenticity revealed they were taken from an Otago Peninsula cave that housed Maori prisoners.
Mr Cull said yesterday the leg irons were historically significant to the prisoners' descendants and should be removed from the open market.
''I decided the most efficient way to do that was to buy them,'' he said.
Dunedin man Steve McCormack, who sold the shackles, said he and his late brother removed them 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 although the shackles were already Dunedin City Council property, it was easier to buy them from Mr McCormack than start legal proceedings.
''We could have spent a whole lot of money going through a legal process, and that is ratepayer money.''
Buying the shackles was more economical, efficient and respectful to runanga than going to court.
The purchase was important for retaining a relationship with Ngati Ruanui runanga, Ngati Mutunga runanga and Parihaka Pa, Mr Cull said.
A relationship between the council, Ngati Ruanui and Ngati Mutunga was created after a 2012 hikoi to Dunedin in memory of the six tupuna [ancestors] buried in the Southern Cemetery.
The North Island descendants and Otakou runanga would be consulted on the future of the shackles.
''They are still ours and we get the final call, but out of respect since it was their tupuna shackled up in the damn things, we will ask them what they would like to see happen to them.''
Mr McCormack said Mr Cull paid more than the initial auction reserve.
''I got what I wanted and a bit more.''
With the money, he had maintained his car, paid some bills, bought his daughter an electric organ and would give his son some cash and would buy some ''fancy'' food.
Mr McCormack believed he had done the right thing by taking the shackles to auction because auctioneer Kevin Hayward was licensed to sell Maori artefacts and relics.
Otakou runanga elder Edward Ellison said securing the shackles was a positive.
Mr McCormack should not have benefited financially, Mr Ellison said.
''They were property of the city, as I understand it, and they are heritage, historic items.''
A Parihaka Pa spokesman, Ruakere Hond, of New Plymouth, said if Mr McCormack believed the shackles had historical significance, he should have surrendered them rather than risking losing a historic artefact to a foreign collector.
Mr Cull stopped the auction of the shackles earlier this month and launched an authenticity investigation after Mr Hond labelled the sale ''obscene and morally repugnant''.
Hayward's Auction House owner Kevin Hayward said the council paid $3500 for the leg irons, plus a 10% commission and GST on the commission.