Four people suspected to be involved in the burning of trains at the Braamfontein train yard last year were detained by Passenger Rail Agency of SA (Prasa) security guards on Sunday.
Prasa spokesperson Nana Zenani said they were detained by the guards on Friday night and were handed over to police at Johannesburg central police station.
They are expected to appear in the Johannesburg Magistrate's Court on Monday, with Transport Minister Fikile Mbalula expected to attend the case.
Further information was not immediately available from the police.
In December, Gauteng Metrorail spokesperson Lilian Mofokeng said the fire destroyed 10 coaches, five motor coaches and five plain trailers - causing damages of about R50m.
The coaches had been waiting to be repaired and were not in service.
In the meantime, Prasa said a cable smelting operation had also been uncovered in Heidelberg.
Three people were arrested in connection with that operation, where cables were smelted into blocks at an illegal facility in Ratanda. One of the suspects is understood to be a Prasa employee. The items recovered were valued at around R2.6 million.
Prasa announced last week that an R1.4 billion project will work on restoring services to the central line in Cape Town. This line is closed due to rampant cable and infrastructure theft. Combined with a stalled MyCiTi N2 Express contract renewal, this has caused major problems for commuters.