Good luck sueing the slovak police... there were cases were real harm was done and it took years to sort it out, sometimes at the european level (I am a Slovak living in Slovakia and following the local news).
Here it looks like the slovak police botched their job, but it took irish officers to make a royal mess of it
The local media coverage (by any means _not_ government friendly) says that
1) the slovak authorities informed the pilot who was still waiting for takeoff and he decided that this is not a threat and continued the flight
2) the Dublin airport was informed during the flight. They later reported back that they did not find any explosive, but the officer informed his boss two days (!) later, triggering the a bit chaotic operation.
From the information circulating I tend to believe that the Dublin airport was sitting on the failed catching of the "parcel" for two days and is doing damage control now.