Late last month, 18 carriages at the station went up in flames. 

Police made a breakthrough this week with the arrest of the two boys.

Untu said they had "serious doubts" that the teenagers are behind the ongoing attacks over the past four years.

The union's Sonja Castens said they had repeatedly asked the SAPS to utilise its Crime Intelligence service to confirm the union's suspicion that a third force was behind the attacks.

Castens said that the rapid rail police unit was failing in its duties.

"If they were identified on CCTV footage, they are most likely the victims of a very well organised third force that's behind all of this. We want the police to intensify their efforts."

The unit provides visible policing to ensure the safety of commuters.

"If you look at the mandate to protect commuters and employees of Prasa, having no assistance from the police is not helping."

Eyewitness News (EWN)