A URINE sample from a drink driving suspect was compromised by being microwaved at a post office, gardai believe.
Officers are probing the incident, in which the sample was sent by registered post to Dublin to check it for alcohol content.
Two post office workers were taken in for questioning in connection with the case.
And it is not thought to be an isolated incident as samples taken at other stations are also believed to have been tampered with on previous occasions.
The bizarre series of events began when gardai took a sample from a man arrested on suspicion of drink driving in the west of Ireland in March.
It was sent by registered post to the Medical Bureau of Road Safety in Dublin for analysis.
When tests at the laboratory returned an alcohol reading of zero, gardai decided to investigate further.
They viewed CCTV footage from the post office in question and last week two workers, who cannot be identified, were arrested.
They were later released without charge but it is believed a file is being prepared for the DPP.
The suspicion is that one of the workers tried to interfere with the sample by microwaving it so that the alcohol content was boiled down.
In such a situation, testing would not have produced accurate results.
Gardai have confirmed there is an investigation into the allegations. They did not comment further.