The investigation into the murder of a Australian-based New Zealander is not making much progress, but it has highlighted local concerns about crime.

A man detained by police investigating the murder of New Zealand tourist Nicholas Heyward in Argentina has been released after witnesses failed to pick him from an identity parade.

Australian-based Mr Heyward, 31, was shot dead when two motorcycle-riding robbers, known as “motochorros”, tried to snatch his bag while he strolled through a park in the city of Mendoza on Monday (local time).

The suspect, who is reported to be either 19 or 20 years old, was arrested on Wednesday and his brother also faced an unrelated firearms charge.

El Sol says the man was released after three witnesses failed to recognise him.

The three witnesses were friends Pierre D’Amico, 29, and Fiona Darling, 34, and an education worker who found himself facing the motochorros.

A further two witnesses were too afraid to help.

Los Andes reported Mr Heyward’s body is expected o be repatriated next Monday or Tuesday.

A protest against crime at the park where Mr Heyward was shot is planned on Sunday (local time), Radio New Zealand reports.

There are also calls for measures to discourage the muggers who travel in pairs on motorbikes, with one riding and the other snatching bags or wallets.

Some cities require motorcyclists to wear high-visibility jackets with identification and ban bikes with two riders in some precincts.

Mr Heyward was shot up to four times between his chest and neck with a .22 pistol, police say.

He had been travelling after finishing a degree in physiotherapy at the University of Queensland and been in Central America for about a year.

He was planning to return in a few months to Australia, where he has family in Adelaide and on the Gold Coast.

Argentina’s Ministry of Security has taken the rare step of offering 40,000 pesos ($NZ5850) to help find the offenders.