As he was transferred through various jails of Russia's vast prison system, Oleg Orlov had a mission: to find out how many political prisoners there were in each facility.
The veteran dissident, freed in August in the biggest Russia-West prisoner swap since the Cold War, knew the lists.
His Nobel Prize-winning rights organisation Memorial has painstakingly recorded the names of people jailed for denouncing Moscow's Ukraine invasion.
The 71-year-old was one of them: sentenced to 2.5 years for speaking out in an article against the military offensive.
But what he found left him in no doubt: Russia has "a lot more" political prisoners than rights groups know of.
On top of the known cases, "in each jail, I found there were just as many people for whom there is a basis to count them as being in prison for politics," he said.
"We knew nothing about them."
Now free and living in Berlin, his life aim is to get them out.
Forced into exile after never planning to leave Russia, Orlov has struggled with his freedom, his mind focused on those left behind.
He often thinks of one cell mate: 29-year-old Alexei Malyarevsky, imprisoned for putting up posters condemning late opposition leader Alexei Navalny's sentence.
"He got seven years. A young man...," Orlov said.
"The feeling is numbing: I am here and he is there."
- 'Hopelessness' -
Orlov managed to avoid "all conflicts" in prison and tried to speak to everyone, intent on finding the people he thought could be considered political detainees.
"There is contact between cells, even if they try to limit it," he said.
He witnessed how Russia's invasion of Ukraine has transformed its massive penitentiary network, with prison authorities trying to "recruit literally everyone" to fight in the war.
He laughed as he recalled how guards tried to recruit him, too.
"I told them: do you understand how old I am and why I am here?"
The issue divided prisoners and Orlov took part in convict discussions on whether it was worth fighting in return for their freedom -- if they survive.
The vast majority of those who joined up, did so wanting a "clean biography and money", he said, rather than out of patriotism.
He also met jailed deserters: three men who told him most of their unit had been killed and that, facing almost certain death, they had decided to run.
Orlov said they were "traumatised psychologically" and, facing a massive sentence, one considered returning to the front to try to regain his freedom.
"It's (out of) total hopelessness," he sighed.
- Wish to go to Ukraine -
Now that he is free, Orlov also has another wish: to travel to Ukraine to see the war that he denounced with his own eyes and document war crimes.
"I hope it will be possible," he said.
He has chronicled war crimes before, dedicating a large part of his work to the Chechnya wars.
"I would like Russian rights defenders to be able to visit Ukraine," he said.
"I think it's very important to get involved in the work of recording the crimes of this war and for it to be done by Russian rights defenders, too."
He did not say at which stage the plans are and it is unclear whether Ukraine would allow it.
Orlov has condemned the invasion since the day the President Vladimir Putin sent in troops in 2022.
He dismissed the notion of huge popular support for the war in Russia, but also said it is not just "Putin's war" and many Russians are enriching themselves on the back of the invasion.
"It cannot be denied that a significant part (of society) -- not the majority but a noticeable part -- are beneficiaries of the war," he said.
- 'Stunned' -
As he travels through European cities, Orlov often blinks and thinks he sees a Moscow street -- still barely believing what has happened to him.
Around 10 days before his release, guards told him to sign a request for presidential pardon, which he refused.
Then he was woken at dawn, told he was being transferred and put in a prison van.
"The doors opened. I was stunned. I thought I would see a penal colony but I saw Samara Airport," Orlov said, referring to the southern city of Volga.
On the flight to Moscow, he was escorted by guards in plain clothes.
"It just looked like they were my friends: I was unshaven, with these big men around me."
Held in isolation in Moscow's Lefortovo prison for days, he became convinced there was a new case against him and wrote a complaint about not being allowed to shower.
He waited for days to hand it to someone, until a prison official came in.
"I ran to him, so happy I could hand in my complaint," Orlov said, but he was instead told his sentence had been cancelled.
Soon afterwards, he was on a bus headed to the airport with other political prisoners.
Despite his jail ordeal, if he could go back in time, he would still speak out from within Russia, Orlov said.
"I would do the same."