Searches conducted at 12 different houses and six hostels led to the arrest of six suspected migrant smugglers, Europe’s policing agency Europol said in a July 18 press release.

Portuguese officers carried out the raids the day prior, saying those arrested were suspected to be part of a "prolific criminal network."

According to Europol, the suspects helped migrants from Asia obtain Portuguese residence permits using fake documents.

The raids and arrests came after a year-and-a-half investigation into the group between France and Portugal with the support of Spain and Germany, as well as forces from Europol and Eurojust.

"The smugglers used a unique modus operandi to carry out their illegal activity: they would abuse an online issuance process of Portuguese residence permits by facilitating migrants to illegally apply for it," stated the Europol press release.

Fake addresses and occupations provided

According to the policing and crime agency, the gang provided fraudulent permanent addresses and occupations for the migrants applying for residence in Portugal.

The migrants themselves already resided in various EU countries, Europol said.

A member of the gang would pick the migrants up in France, then drive them in a hire car to Portugal to attend the residence interview.

Afterward, Europol believes the members transferred the migrants back to France "via small mountain passes to avoid law enforcement detection."

The migrants could then continue their journeys within the EU "with their newly acquired documentation," Europol said.

French authorities say they have already intercepted 18 smugglers from this network on the French-Spanish border heading to Portugal. They have also intercepted 150 migrants.

Joint investigation

Following the joint investigation, officers found that the network had rented at least 337 vehicles in the last 18 months. Investigators believe that would have allowed them to transport as many as 6,000 migrants through the process.

Authorities believe the fraudulent application process cost individual migrants €10,000 each, with transport between France and Portugal costing between €200 and €400 per person.

Information on human trafficking is available here.