In Madrid's Puerta del Sol square, a small group of Spaniards waved the flag of Novorossiya, the territory once ruled by the Russian empire that encompasses swathes of modern day Ukraine. With the Russian revolutionary symbol of the hammer and sickle fluttering behind them, they denounced the arrest of eight Spanish nationals for fighting with the pro-Russia militia force the International Brigades of Donbass — the first police operation on European soil against foreign civilians who have joined the separatists in the country's conflict-ravaged east.

The men, aged between 20 and 30 and hailing from six different Spanish provinces, were arrested in the first phase of the ongoing Operation Danko, a series of swoops beginning early on Friday morning. The self-styled "anti-fascists" have since been released on bail, but charged with jeopardizing the neutrality of Spain abroad, with alleged crimes of cooperation or complicity in murders, and, in some cases, of possessing weapons and explosives.

Sergio Becerra, 30, told VICE News that he was sleeping at home that morning, about two months after his return from Ukraine, when the doorbell rang. "The next thing I remember is a group of hooded policemen who entered the house without giving any explanations whatsoever. They just asked my name and whether I had been in Ukraine." Sergio responded that he had, since he believed he had "nothing to hide." The policemen searched every single piece of furniture, but found no weapons in his house, he said, adding "that's impossible, I don't own any." They did however find uniforms and military badges the United Armed Forces of Novorossiya, the Russia-backed rebel alliance comprised of the Donbass and Luhansk People's Militias. The force aims to bring the region firmly back into Moscow's orbit; Vladimir Putin has consistently referred to it by the long-buried name of Novorossiya, breathing new life back into the notion of this Greater Russia.

Ramiro Gómez, a spokesman for Madrid Committee in Support of Anti-Fascist Ukraine, speaks at the protest against the arrests in Madrid. Image via Eliezer Sanchez/DISOpress.

At the police station, Becerra found his former comrades. But he insists they were unfazed by their arrests. "We were quite calm. I thought: I've come from a war, this doesn't scare me at all."

Shortly after the arrests VICE News spoke with Becerra and another of those arrested, Hector Arroyo, who had arranged to meet 50 others in the Puerta del Sol to protest their detentions. With them was Ramiro Gómez, a spokesman for Madrid Committee in Support of Anti-Fascist Ukraine, who admitted to having traveled to Luhansk, but only for "humanitarian work," he said. At the end of the demonstration, a Luhansk refugee woman, now living in Spain, approached us. She told Becerra that they had the "support" of the population and that "what you are doing means a lot to us." His swarthy, bearded face lit up. "We also felt this support when we were there, madam," he answered, visibly moved.

Sergio Becerra and another Spanish militiaman in Ukraine last fall. Video via YouTube

Becerra acknowledged that they "received military training" but stressed that he and his companions were not mercenaries, telling VICE News that "nobody has been paid in the popular militia, and that those who travel with them are clearly going to suffer cold and hunger." But, he said, it was "worth it," characterizing his involvement in the conflict as "an ideological struggle against those who fight in exchange for money, such as the mercenaries who fought against our units" — a reference to pro-Ukraine volunteers. Fighters with the rebels do in fact also now receive salaries — around $350 a month for a regular soldier and around $450 a month for a general — though they often report that the payments do not come on time or at all.

He told VICE News that he had left a "job as a restorer of luxury cars where he earned good money" — and "then went bankrupt" — because he "couldn't bear to see people massacred" and because "slaughters and crimes against humanity are being perpetrated in Donbass." Convinced he "was doing the right thing," Becerra is now receiving "support and communication" from the commander of the 404 Unit to which he still belongs while he waits for police investigation to conclude. And he has just has one thing on his mind: "I will go back to Donbass as soon as I have the chance."

The first Spanish-translated videos of Russian propaganda appeared on YouTube in late February 2014, around the time that the former Ukrainian President Viktor Yanukovych fled after being overthrown by the Maidan protest movement. These videos support the Russian version of the conflict and demonize the Ukrainian side, which they brand "Kiev's fascist junta." Becerra and Arroyo, as well as other foreign militiamen, gradually began to appear on such videos, narrating their own experiences in the conflict. Meanwhile, the Spanish authorities were watching closely, the Minister of Interior revealed following Friday's arrests.

Soon, the first Facebook groups appeared, asking for donations for humanitarian aid. Since then, the war videos have multiplied across social networks, some of them containing images of brutal violence. The videos include interviews with Spanish volunteers, exhibited by the Russian media as evidence of international support for Moscow's cause in Ukraine. It was such footage, and word of mouth within Spain's anti-fascist circles, that propelled the Spanish fighters into the conflict.

Two Spanish hooded volunteers on a pro-Russia YouTube channel run from Donbass.

"I learned about the militia through Sergio and other friends," Arroyo, a 27-year-old from Madrid, told VICE News. "I'm saying this because many people think this belongs to communist circles, new parties and recruiting networks [as the judicial inquiry suggests], but that's not true. I'm no communist, and I support neither Putin nor Russia. I'm sharp, skinhead and anti-racist, and I decided to go to Ukraine to help people." Yet the 404 Unit with which he and Becerra fought does support Russia; it is coordinated by Essence of Time, an ultra-nationalist USSR-nostalgic Russian group whose aim is to re-establish the Soviet Union.

Unemployed when he decided to leave for Ukraine last fall, Arroyo took a plane first to Moscow, then to Rostov, just across the border from Ukraine. There he was welcomed by a "militia contact" who took him to the frontline in a bus. Arroyo said he has traveled through "ghost towns" in the conflict zone, and seen families who visited Luhansk's main hospital daily "to get food and clothes." He avoided questions about weapons and specific acts of war, explaining "we are being investigated for this issue and, although nothing can be proved, I prefer not to talk about it." He recalled "how difficult it has been to communicate" without speaking Russian and having to speak in English "to almost everyone." But, Arroyo added, he was far from alone in this: "I also served in the Continental Brigade, and I found many French and Serbians there."

The next trip of the Spanish "international brigades" is due to depart on May 9 — "should the police allow us to [go]," Arroyo said. The Madrid Committee in Support of Anti-Fascist Ukraine has called a humanitarian convoy planned for that day, which will travel to Luhansk from Italy. Gómez, the spokesman, said he believes that the "fairest" thing to do is to continue supporting the cause openly. "That's why we'll be going back," he said. Gómez also appears in several videos and social media posts, explaining his role in "humanitarian work" in the region. He says he has witnessed "both dead mothers and children as well as destroyed families and houses" during his trips to the region.

Many Ukrainians living in Spain consider these activities nothing more than propaganda in support of the Russian invasion of their country. One of them is Lilia Nikolayev, 27, a promoter of the ConUcrania.com website. Alongside many other similiar initiatives, ConUcrania represents hundreds of Ukrainians whom, like Nikolayev, have spent "a long while looking for support and pursuing peace." They say groups such as Essence of Time and other Russophile organizations have created a pro-Russian propaganda network in Spain.

Ramiro Gómez, right, in a pro-Russian video in Spanish. Video via YouTube.

The government could have trouble making the charges against the Spanish fighters stick, experts say. Manuel Cancio, a criminal law professor at the Autonomous University of Madrid, said he believes the charges announced by the Ministry of Interior have "no legal basis." Regarding the charge of jeopardizing Spain's neutrality abroad, he said it would be difficult to prove that that the actions of the defendants had such an impact as "they are just eight people acting according to their free will." "Wars are now asymmetrical, not necessarily involving one state against another as it used to be in the past," Cancio added.

The professor said it would also be "really complicated" to prove the murder charges against the Spanish fighters, particularly as Ukrainian legal and constitutional frameworks in which the fighting was taken place had to be taken into account. "This is extraordinarily difficult," he explained.

In legal terms all of the charges were "weak," Cancio said. They also depended greatly on your definition of what was a lawful act of battle and what was criminal, or terrorist, he explained — something that varied greatly from country to country. The professor pointed to cases of Spaniards who had joined the Kurds in fighting the Islamic State in the Syrian town of Kobane. They had been involved in comparable actions, he said, "but no one called them terrorists or criminals."