Police have detained four people in Gurkovo during an operation, Sofia police chief Nikolay Peltekov told reporters. Chief Commissioner Peltekov heads the Sofia Directorate of the Interior (SDVR). The four are aged between 31 and 54.
Police are checking whether they are linked to a Sofia police investigation into illegally used tracking devices.
No charges have been brought against the detainees so far.
The SDVR has opened pre-trial proceedings because a special technical device was used illegally to gather information outside the legal procedure. The report came from the people the devices were used against. They had suspicions, and SDVR officers found the devices.
A report was also filed with the Interior Ministry's regional directorate in Stara Zagora. But the case is run in Sofia because the first report went to the SDVR, Peltekov explained.
Expert examinations are due to show exactly what the devices were used for, the chief added.
Once the experts report, the materials will go to the Sofia District Prosecutor's Office.