Finland's National Bureau of Investigation (NBI) has concluded a preliminary investigation into hazardous waste trading that saw dangerous materials exported from Finland.
The investigation includes three separate instances involving some of the same suspects, who have been investigated on suspicion of aggravated environmental degradation.
In total six people are suspects in the investigation, and seven companies are linked to the probe.
The NBI said in a statement that their inquiries began after a shipment was stopped by Estonian authorities in Tallinn harbour.
The cargo contained fine aggregate, rather than building waste as was on the ship's documentation, and it cannot be disposed of in the same way.
After starting the probe, officers found evidence that 860 tonnes of transformer oil had also been shipped from Finland without permission, along with other hazardous waste.
The NBI said that illegal shipments of hazardous waste are on the increase.