GENEVA — The 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.’ ”