By Olga Prosvirova & Zhanna Bezpyatchuk
BBC World Service
Volodymyr Buzynov has been searching for his brother Mykyta for nearly two years. Mykyta is one of thousands of Ukrainian civilians being held in prisons in Russia and the occupied territories for opposing the war. But with no charges, formal investigation, trial, or release date, their location is a mystery, and unlike prisoners of war, there is no formal mechanism to secure their freedom.
Warning: This story contains descriptions of torture
When Russia invaded Ukraine in February 2022, the Buzynov brothers, their mother, and Mykyta's girlfriend fled their home in Chernihiv in the north of the country to avoid the conflict. They went to the village of Mykhailo-Kotsiubynske, but by early March, Russian soldiers arrived there too. "We've come to liberate you from your government. Putin is cool," the soldiers exclaimed.
Volodymyr says the soldiers searched the village, confiscating phones and accusing his family of sharing the location of the Russian army - something they all deny. Then, Volodymr says, the soldiers set up what sounded like a fake execution.
"They took my brother Mykyta and others behind some trees and told them to line up against a wall, yelling: 'Get ready! Aim!' Then they took Mykyta's girlfriend Kateryna, and made her kneel next to him. Aiming a rifle at her head, they said to my brother: 'If you don't confess, we'll shoot her.'"
Volodymyr says that was the last time he saw Mykyta. "He may have confessed to save his girlfriend because they let her go. They told us: 'He admitted everything. He's facing up to 15 years in prison.'"
According to the Ukrainian government, as of November 2023 there were 4,337 Ukrainians in Russian captivity. Most were military personnel, but 763 were civilians. However, there is no official list of their names and Ukrainian authorities rely on data from the Red Cross.
The Red Cross can't always gain access to the places where Ukrainians are held in Russia, let alone in the occupied territories where unofficial detention facilities can include basements in hotels and abandoned buildings. The Ukrainian Parliament Commissioner for Human Rights Dmytro Lubinets says that the figure could be much higher, with a total number of missing civilians estimated at 25,000.
The BBC has asked the Russian defence ministry to disclose how many Ukrainian civilians are being detained and where they are being held but we have had no response.
Under Russian law, a person can only be detained for 48 hours without a court order and records must be kept. Last year Russian President Putin extended the period to 30 days in occupied areas of Ukraine for serious offences or violating wartime prohibitions or restrictions.
But often the time, place and grounds for detention are not being recorded, no criminal or administrative cases are opened, and no investigations are conducted, according to court papers reviewed by the BBC.
Anastasia Panteleyeva from the Media Initiative for Human Rights (MIHR) says Russia is justifying the detention of Ukrainian civilians under the broad term of "resisting the special military operation".
"A person can be arrested just because the windows in their house overlook an area of potential importance to the Russian military. And if the soldiers get shot at, the person living nearby gets blamed," she explains.
The Russian Ministry of Defence argues captured Ukrainians are "being held in accordance with the requirements of the Geneva Conventions on the treatment of prisoners of war".
The Geneva Conventions prohibit the taking of hostages but say nothing about taking civilians prisoner, only military personnel.
They say non-combatants can only be detained "in accordance with the laws and rules of the occupying side" and with the guarantee of due judicial process.
Lawyer Polina Murygina, who assists captives through her project, Every Human Being, says: "Finding someone in the system, let alone extracting them from it is very difficult. We have come across a legal paradox - it's better if they think you're a criminal."
When a person is charged they appear in the system and have rights or if they are prisoners of war, they can be exchanged. But captured civilians end up in detention without a defence, charge, or trial.
Tracking Mykyta down
Desperate to track Mykyta down, his friends and relatives started to use the prisons letter service, which allows you to send messages to some penal colonies and investigative isolation units.
Eventually they received a response confirming he was being held in a pre-trial detention centre called SIZO-3 in Belgorod, just over the border in Russia. But when a lawyer went to visit, the prison said nobody of that name was there.
Another lawyer, Leonid Solovyov, says this is a regular occurrence: "Pretty often, I arrive and they tell me the person isn't there. Either they just won't let me in, or the person has in fact been relocated. You can't go there and expect to be able to check all the cells. You have to rely on the answer you get at the door or, in the best case, from the prison chief's office."
The BBC also tried to track Mykyta down. We wrote to SIZO-3, Penal Colony 4 which is also in the Belgorod region, and other institutions where human rights activists believe Ukrainian prisoners are being held.
Most institutions came back saying they did not have any such prisoner. However, SIZO-3 said the message had "cleared censorship and was handed over to the addressee" - this should have meant Mykyta was there, but a day later we received the same response from Penal Colony 4.
As the long and frustrating hunt for Mykyta continues, the BBC has managed to speak to former detainees. Often their stories paint a grim picture, with one prisoner saying Ukrainians in Russian prisons are treated "like sub-humans".
Anton Lomakin, a police officer in Kherson, was not able to get away when the Russian invasion began, so he hid. Then in the summer of 2022 he also disappeared and his family could not find him.
Anton says he had gathered some information which he passed on to the Ukrainian military. He says he was betrayed by a colleague who was bringing him supplies, captured by the Russian army and taken to a temporary detention facility in Kherson.
"During the journey they used a taser on my legs and other parts of my body. They staged a mock execution and led me out to a hole in the ground. They made me kneel and told me to pray.
"They loaded their guns and fired just past my left ear. There were three or four short bursts. Then a mobile phone rang, they put it on loud speaker and someone at the other end said not to shoot me."
Anton says when he got to the centre, he was interrogated, beaten, threatened, and doused with cold water, almost causing him to choke. His account matches the testimony of other prisoners held at the institution at the time the city of Kherson was occupied by Russian forces.
"One time, they told me to lift my legs with my heels up. I refused. They put a gun to my genitals and gave me a choice. Of course, I chose to raise my feet," Anton says.
"They took two rubber truncheons and bludgeoned my heels with them for a long time. Any time I lowered my feet, I was made to lift them again. Otherwise they'd beat me, hitting my head and back," he recalls.
The BBC has asked the Russian Ministry of Defence about Anton's case and is waiting for a response.
Russia does not acknowledge holding civilians as captives and has previously denied accusations of aggression or crimes against them.
Anton says he shared a cell with seven other men: one was a former Ukrainian police officer, and another lived in the centre of Kherson, near the building where Russian military were stationed. Both were accused of being Ukrainian intelligence agents. The other cellmates could not explain why they had been imprisoned.
Anton was transferred twice and his family was only able to locate him with the help of a friend who had a Russian passport.
He was finally released after 104 days, penniless and without documents.
The Ukrainian police and the Office of the Prosecutor General of Ukraine consider the detention of civilians a war crime and are involved in searching for missing or abducted people.
Irina Didenko from the prosecutor's office says that "90% of those detained are subjected to torture".
In international law, there is no specific mechanism for freeing civilians from captivity. The Geneva Conventions state that a combatant can only be exchanged for a combatant. You can release a civilian, but not in exchange for someone who is a soldier.
"Potentially, the best way to release and repatriate civilian hostages might be through a third party state," says Didenko. Middle Eastern countries have already negotiated exchanges of prisoners of war, the return of deported children and civilians and the release of foreigners from Russian captivity.
When it comes to the United Nations (UN), human rights activists argue its mechanisms are outdated, saying - UN documents do not cover this kind of "detainee".
And for people like Volodymyr, who dreams of being reunited with his brother Mykyta once again, hopes are fading fast. "There's nowhere we haven't turned to," he says.
"To start with, we had the illusion that we'd get help from international organisations. But all we got from them was: 'Registered. Received.' We never got further than that."