A South Korean national who fled to New Zealand after allegedly murdering three family members arrived in the country flush with $100,000.

Police emails about the case, released to the Herald on Sunday, reveal when Sungkwan Kim landed in Auckland on October 24 - three days after the killings- he declared $101,240 to border officials.

Police initially redacted the figure but North Shore crime investigation branch's Detective Sergeant Ash Matthews later confirmed the amount, given the wide publicity of the case and Kim's confessions to South Korea officials.

South Korea media reported Kim confessed he killed his mother, half-brother and stepfather because he was in financial difficulty. Their bodies were found with stab wounds in an apartment and a car boot.

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He reportedly withdrew 120,000,000 South Korean Won from his mother's account, the equivalent of $153,000, telling police he was financially struggling after his mother remarried and their relationship soured when he repeatedly asked her for money.

It's understood he later spent the money on a luxury car and appliances for an Auckland home he moved into with his wife and child, with South Korean media reporting he paid cash.

Matthews said since Kim's extradition earlier this month, roughly $35,000 of the $101,240 he brought into New Zealand had been seized by South Korea officials and the rest would be travelling back with Kim's lawyer.

"I assume that will be seized on arrival," Matthews said. "Obviously some has been spent and won't be retrievable."

Kim, a New Zealand resident, was arrested three days after his arrival and agreed to extradition after making appearances in the North Shore District Court for historical theft charges from previous time spent in Auckland.

The emails reveal police considered charging Kim with money laundering but Matthews said he decided against it because it wasn't in the public interest. It would have delayed his return to South Korea to face more serious charges, based on the same facts, he said.

"In summary, involvement of the police in this matter was assisting the court and relevant authorities in terms of his surrender to Korea. This was essentially finding him, and executing the extradition warrant, then making the practical and logistical arrangements for his return," Matthews said.

"It so happened that he had the outstanding theft matter here which simplified matters for us somewhat in terms of his custody."

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Kim was extradited in January to face charges including murder, abandonment of a corpse, and fraud.