Raphael Minder of The New York Times reports police in Europe have dismantled a criminal network that was selling horse meat across the Continent that was “not suitable for consumption,” arresting 66 people as part of a four-year investigation prompted by the discovery in Ireland of horse meat in burgers sold as beef.

Europol, the European Union’s law enforcement agency, said on Sunday that all but one of the arrests had been made in Spain. But the Spanish police said in a separate statement that their part of the investigation had accounted for “a small portion of a network stretching across the whole of Europe, under the control of a Dutch citizen.”

The Dutch citizen, who has not been publicly identified and was taken into custody in April in Belgium, was described in a Europol statement as the leader of a criminal gang that had acquired horses on the Iberian Peninsula that were judged to be “in bad shape, too old or simply labeled as ‘not suitable for consumption.’ ”

The animals’ meat was processed and sent to Belgium, one of the European Union’s biggest exporters of horse meat, and the criminal organization modified the animals’ microchips and documentation to facilitate the fraudulent export, the statement said.

The Pan-European investigation began after a scandal over horse meat in burgers in Ireland in 2013, and it was widened to other European countries as dishes like frozen lasagna labeled as containing beef were found to have horse meat.

In addition to the arrests, the Spanish police said on Sunday that they had seized property and luxury cars, and that they had frozen bank accounts. The police in Britain, France, Italy, Portugal, Romania and Switzerland also carried out interventions, according to Europol, although the statement did not provide details.