Along with war trophies and plunder from private homes that even included toilets, they dragged off hundreds of captured Ukrainian civilians, most of whom remain incarcerated to this day in jails scattered across the vast Eurasian landmass.

Natalia Yaschuk, a senior manager at the Kyiv-based Center for Civil Liberties, is tasked with identifying and locating these hapless victims of war, in the hope of one day bringing them home.

“Sometimes you had a person who was detained and imprisoned just for bringing water to a village that had been cut off because of fighting,” she recounted.

The centre has identified around 200 ordinary non-combatants who were forcibly taken to Russia from the scores of villages and small towns that surround the Ukrainian capital, and 1800 more taken from other parts of Ukraine who are being held in Russia or Russian-held territory.

Altogether, Natalia estimates there are as many as 16,000 Ukrainian civilians languishing in Russian-controlled jails, prisons or penal colonies.

She said: “There was one woman, a 25-year-old schoolteacher from Kyiv Region, who was imprisoned for six months at a remand centre in the Russian Kursk region for texting her sister that she had seen Russian tanks in her town.”

The vast majority of those detained are treated as criminals, she said: “They are charged with spying or terrorism and often kept isolated from each other.”

The vast majority of those detained are treated as criminals, she said: “They are charged with spying or terrorism and often kept isolated from each other.”

In Russia alone, there are upwards of 100 different places where civilian prisoners are held.

“They spread them out across institutions so that they cannot support each other.”

After the civilian POWs are located, the centre attempts to contact them, connect them with their families and advocate for their release, often using Russian human-rights groups to provide legal services.

“These groups help us locate our people and help them to survive, but there is always concern about who we can trust,” Natalia said.

Even when a prisoner is located, gaining access is difficult to impossible, she added.

The bureaucratic process, which usually begins with people reporting a missing family member to police or prosecutors in Ukraine, is long and difficult, leading some to try and make contact on their own.

“The scariest thing is when our people turn to NGOs infiltrated by the FSB or Russian state agencies themselves, who end up manipulating them, sometimes against Ukraine,” she said.

Natalia’s and other NGOs try to help prisoners’ family navigate an otherwise complicated and intimidating journey.

She said: “Being identified and located is important in itself as it lets the world know you exist.”

But what happens to prisoners during captivity explains why the Russians have no interest in acknowledging their existence.

Natalya said electric shock, torture and beatings with trudgeons and sticks are standard practices when prisoners are first detained.

“You can always see when they have been repeatedly electrocuted because scars remain where the wires were connected to the chest,” she said.

Skin infections and tuberculosis are also common among returnees.

The psychological scars former detainees bear are often worse.

“Many suffer from survivor’s guilt,” she said, and rehabilitation is lengthy.

Relatively few, however, have been released – around 400 in four years of war – some in exchanges, some in body bags.

“The Russian Federation doesn’t want to release them because their detention is an international war crime,” she said.

“They take someone from a house, say ‘don’t worry, we’ll return them in a week’ and they still haven’t returned after four years,” she added.

Life for both prisoners and family members becomes a waiting game.

For Natalya, who has been trying to speed up their return for four years, while her own husband serves in the army, “The greatest challenge is to wait for my people to come home.”