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Mr Heyward, 31, was killed on Monday by motorcycle bandits who shot him four times.
He died in the arms of his friends, while the assailants fled into the suburbs of west of Mendoza.
The Buenos Aires Herald reported this morning local police had one person in their custody following raids in relation to the attack on Mr Heyward.
"There were raids today and we have detained one person in connection to the crime" provincial police chief Juan Carlos Caleri told the Buenos Aires Herald.
"At this stage I cannot give further details, though we may be able to release more information tomorrow. The person is being treated as a suspect," Mr Caleri said.
After the offer of a 40,000 pesos ($5800) reward for information leading to the capture of the assailants, a witness came forward on Monday night.
Mr Heyward was born in Australia but his late mother was from New Zealand. He also travelled on a New Zealand passport.
His father Ben told Australian Media his son, a trained physiotherapist, was a great adventurer and spent a lot of time travelling - frequently returning to visit family here, including a trip last year to see his grandparents.
"He was a bold spirit, loved music, and a good man. He was a good listener, a great encourager and loved his brothers, family and friends," Ben Heyward told the Sydney Morning Herald.