When the company was liquidated, it was revealed investors were owed $2.7 million.
The following year the SFO laid 17 Crimes Act charges of theft by a person in a special relationship and 12 charges of false statement by a promoter.
Kairua has now has pleaded guilty to 13 of the 17 theft charges, and 9 of the 12 false statement charges. The rest of the charges have been withdrawn.
At this sentencing at the Auckland District Court this afternoon, Kairua represented himself and detailed the background to the business' demise.
Kairua said he was "well and truly duped" by his former trader Elijah Geldman, who was jailed in the United States for an unrelated fraud.
After firing Geldman in September 2011, Kairua took over the trading himself but was inexperienced in dealing with precious metals.
Kairua told the judge he believed Geldman should be with him in court today.
"I'm not a conman your honour. I haven't run away....I'm not hiding assets," Kairua told Judge Christopher Field.
Nick Williams, for the SFO, said the gold trading "was a bogus, fraudulent scheme" from the start.
Williams said Kairua tried to cover up losses by using new money to pay other investors in a ponzi-type scheme.
"He has his eyes open as this was happening," Williams said.
Judge Field, in sentencing Kairua, said the losses arising out of the offending was some US$1.5 million.
While he was duped by Geldman at the beginning, Kairua "became responsible for the running of the company", Judge Field said.
"The time must have come when you knew the company could not continue operating in the way that it did. That is the time you should have called a halt and you did not. You continued trading, continued taking money from people and continued promoting the company," the judge told Kairua.
There was no doubt that the offending was premeditated and even if there was the option for home detention, the circumstances demanded a prison sentence, the judge said.
After giving Kairua a discount of 11 months for his guilty plea and four months for previous good character, Judge Field sentenced Kairua to 3 years, 9 months in jail.
During the hearing, the judge acknowledged the distress the offending caused Kairua's victims.
"I hope that for them this could be seen as the end of a long and personally distressing road for them," he said.
John Fraser, whose family lost the $340,000 they had invested with BullionBuyer, said he was "very happy" with the outcome.
"I don't like to see anyone put in prison but as long as he's not stealing other people's money and ruining their lives I think it's a positive thing." Fraser said.
