Thanks to the Russian nerve agent "Novichok," I once got to see the inside of an interrogation room at Lefortovo, the old KGB prison on the east side of Moscow.
It was in 1993. The Russians were not pleased that I had written an article the year before disclosing the existence of Novichok, identified today by British investigators as the weapon used last week in the attempted murder of former Soviet spy Sergei Skripal and his daughter in Salisbury.
The nerve agent was top secret back then, especially sensitive because the Soviet Union, under Mikhail Gorbachev, had renounced the use and production of chemical weapons.
Its existence came to light thanks to the scruples of a brave scientist named Vil Mirzayanov, who had worked at the State Union Scientific Research Institute for Organic Chemistry and Technology.
The institute was described by one its top officials as "the leader in the technology of chemical destruction."
On a grey September afternoon, Mirzayanov and a scientist-activist named Lev Fyodorov came by the Moscow office of the Baltimore Sun, where I was working.
The Cold War was supposedly over, and Mirzayanov had been growing more and more angry over the secret weapons work.
He decided to go public, and the two scientists told me that they had arranged to publish an article the next day in the Moskovsky Novosti newspaper.
But, they said, they thought they could ensure some measure of security for themselves by also getting the story out in the West.
After all, they reasoned, the United States and Russia were on friendly terms, American aid was crucial to Russian stability and no one should have any need of nerve agents.
They told me Russia had a nerve agent 10 times more powerful than VX, a powerful chemical weapon, and that work on it was continuing.
I wrote a story that day after checking in with Western experts, who were sceptical of the claim - to put it mildly.
But in the month that followed, I tracked down more scientists who worked at the institute and wrote a fuller story that named the new agent: Novichok No. 5.
I learned that research on Novichok had begun in 1987, even as the Soviet Union said it would unilaterally halt all its chemical-weapons programmes.
It had been developed at the institute and tested in a place called Shikhani, in southeastern Russia, and in the Nukus region of Uzbekistan.
I spoke to one scientist, Andrei Zheleznyakov, who had been exposed to a minute amount of Novichok in a lab accident five years prior.
He staggered out after the mishap, his vision, as I wrote, "seared by brilliant colours and hallucinations." Zheleznyakov never fully recovered, and he died shortly after I interviewed him.
The Russian Government, by then under Boris Yeltsin, said that it had never renounced doing research on chemical weapons strictly for defensive purposes.
It said Russia was not stockpiling Novichok, which explains why it had not felt obligated to report its existence under chemical-weapons conventions.
"We played the game under the agreed-upon rules," I was told by General Anatoly Kuntsevich, Yeltsin's adviser on chemical and biological disarmament.
In 1993, Mirzayanov was arrested and charged with divulging state secrets. (He was not allowed to know the specifics of the charge, which was itself a state secret.) He was held for months in pre-trial detention. During that time, I was summoned by the successor agency to the KGB to appear for an interrogation at Lefortovo.
I was allowed to bring my own translator, so I asked Andrei Mironov, a mutual acquaintance of me and Mirzayanov, to accompany me. He was a former dissident and political prisoner who had no fear of the security services.
My interrogator was Captain Viktor Shkarin. He asked if I minded if he smoked. I said I did, which seemed to agitate him quite a lot. The interrogation room smelled strongly of old cooked cabbage.
It quickly became evident that Shkarin was trying to maneuver me into giving testimony he could use against Mirzayanov.
He would ask a question; Mironov would translate it - though I could generally follow along; I would answer in English; Mironov would translate that, frequently giving me advice on how to answer.
Then Shkarin would turn to an ancient word processor and write out a question that wasn't really the question he had just asked, along with an answer that was quite far from the answer I had given. Then we would fall to arguing and negotiating over language. This continued all day. In the end I refused to sign the protocol of the interrogation.
Shkarin threatened to keep me in detention, but Mironov said he would sign it as my interpreter - and it's a good thing he did. Months later, when Mirzayanov was on trial and the Russian Government was desperately looking for an excuse to drop the charges against him - the United States and Germany were pressuring Moscow over the case - Mironov was able to use his standing as signatory to declare that my protocol was an unfaithful transcript.
Presto. Mirzayanov walked free - and walked home, because he didn't have bus fare.
Sometime after that, Mirzayanov moved to New Jersey and took a position at Rutgers University. In 2000, I wrote a follow-up story about a joint US-Russian programme to destroy the last of Russia's chemical weapons. Apparently, it didn't take.
- Englund is a veteran Moscow correspondent and an editor on the Washington Post's foreign desk. A winner of the Pulitzer Prize, he is the author of March 1917: On the Brink of War and Revolution. Follow @will.englund.