Boris Karpichkov, a former senior KGB agent, spent 15 months in New Zealand in 2006 and 2007 after working as a double agent in the 1990s and passing information to the West.
He has said he was walking down Queen St in 2006 when someone threw powder in his face and he later became seriously unwell.
"I just was walking ... and just noticed with side vision that some person approached me. He looked like a common beggar and tried to grab my bag.
"Next what I felt was a kind of dust was thrown into my face ... and the beggar just walked away.
"I walked around 1500m and then almost passed out because my head started spinning. I started sweating. Later that evening, my nose started running."
A doctor told him he had the common flu.
He said he was a 90kg "fat man" when he arrived in New Zealand, but after the dust attack he lost 30kg and his body hair started falling out. His health has since stabilised.
A police spokesman confirmed Karpichkov was in New Zealand between June 2006 and October 2007.
"We are currently examining our files to assess what information we may hold about Mr Karpichkov," he said.
Karpichkov was a Russian spy in Latvia, but in 1995 began passing information to the Latvian Government and its Western allies. When he was discovered in 1998, he fled to London.
