The group is suspected of having modified the horse's microchips and documentation to pass off the meat as edible.
They worked in co-ordination with Belgium, France, Italy, Portugal, Romania, Switzerland and the UK, Europol said in a statement.
'The meat was distributed in different ways but mainly sent to Belgium, the largest exporter of horse meat throughout the European Union, ' said a police spokesman.
He was first sought in connection with a scandal in the Republic of Ireland in 2013, when horsemeat was found in beef burgers, but his whereabouts were unknown at that time.
The suspects are facing an ongoing criminal investigation led by a court in the northern town of Ponferrada, in the Spanish province of León, into alleged animal cruelty, forgery, money laundering, membership of a criminal organisation and a crime against public health.
Authorities allege horse meat was being sold that was unfit for human consumption.
The investigation in the wake of the scandal let to "the identification of a Dutch citizen known in the horsemeat world", Europol says.
This marked the start of an investigation to find the origin of the contamination.
Last summer, police noted "unusual behaviour" in the horse meat market and arrested the original ringleader in Belgium although he was living a "discreet" life in Alicante. "From there he led the activities of the organisation, putting his most trusted men in charge in every country affected by the scam".
Old, unfit or just unwanted horses were deliberately targeted in Portugal and the north of Spain and put down in two concrete slaughterhouses, police say.
He was subsequently arrested in Belgium.
An official for Spain's Guardia Civil inspects a slaughterhouse in Spain. The investigators then determined the organization was involved in more countries than Spain. Europol added that it had seized bank accounts, properties and luxury cars in the course of the investigation. The results concluded that the destination of the horse meat was mainly outside of Spain, due to the fact that the samples in Spain matched those found overseas.