Mpumalanga police are under investigation after dagga with a street value of R4 million, kept inside a cell at Mahamba police station near Piet Retief, went missing last week.
Police spokesman Constable Eric Sibisi said they had handed a docket over to the organised crime prevention unit.
"We have submitted all the relevant documents to the unit and they will be working on it soon. Everyone will be waiting for their report.
"I am adamant that the organised crime prevention unit will easily find out if our officers assisted in stealing the dagga. At this stage we can't say if our police were involved or not," said Sibisi.
He was quoted in a local newspaper as saying: "We suspect that it might be an inside job because the officers who were on duty claimed they did not hear anything at the time of the theft."
It is believed that the culprits made off with 37 bags of dagga that were kept inside the police cell.
Sibisi said the criminals had managed to break open two doors of the cell to get inside.
He said police were certain that the dagga was taken to Swaziland because the border fence that separates the two countries (Swaziland and South Africa) was damaged.
"Investigations revealed that the suspects had dragged the bags from the police cell and across the border through the broken fence.
"The police station is situated just 300 metres from the border fence that is why it would be so easy to get the bags into Swaziland," said Sibisi.
"If necessary we will communicate with the police in Swaziland to help us arrest the thieves. At this stage we cannot say if the perpetrators are from a particular country, but we are sure that the dagga was taken to Swaziland," he added.
The dagga was kept in the police cell after it was seized by the police from smugglers trying to sneak it into South Africa from Swaziland.
Sibisi said that cases where people were arrested for dealing in dagga was a "daily headache" for the police working at the border posts.