The two were arrested at OR Tambo airport last year after being found in possession of rhino horn worth R4.5 million.
The suspects appeared in court on January 23, but their names were not be revealed “for security reasons”.
Police believe the suspects had ties to big rhino poaching syndicates operating within South Africa and internationally, Hawks spokesperson Hangwani Mulaudzi told The Citizen.
The suspects were “cooperating with authorities”, he said.
However, it has not yet been established whether the 18 horns seized were poached from rhino within South Africa’s borders.
“All necessary security checks on the suspects and rhino horns has been done. We are awaiting results,” said Mulaudzi.
At the time of the arrest, police suspected the horns had been taken from rhino in the Kruger National Park.
The suspects were arrested in October after allegedly trying to smuggle about 41kg of rhino horn to Hanoi, Vietnam.
Read more: D-Day for Vietnamese rhino poachers
The men were booked on a Qatar flight from Maputo, which made a one-hour scheduled stop at the Johannesburg airport.
The passengers were asked to exit the flight because authorities had received a tip two men on board were travelling with the horns.
A specially trained South African Revenue Service detector dog reportedly reacted positively to the suspects’ luggage.
At the time, a police spokesperson said it was “the largest haul of rhino horns seized in one operation in South Africa”.