"I'm Arkady Babchenko's murderer," Tsymbaliuk told Jonah Fisher, a correspondent for BBC, as they met in a Kyiv cellar.
An active member of one of Ukraine's right-wing groups, he has been a volunteer in the war against Russian-backed rebels in the east.
Has he ever killed anyone? It's an uncouth question, he told Fisher.
In early April, Mr Tsymbaliuk says he was approached by fellow Ukrainian Borys Herman to carry out an assassination.
Through a combination of face-to-face meetings, instant messaging, and a cash advance of $14,000 (£10,400) they allegedly made plans to kill Mr Babchenko.
A contact from his time in the east, Mr Tsymbaliuk says he thinks he was chosen because Mr Herman, a weapons manufacturer, thought he could be easily manipulated.
If that is true it was a bad miscalculation: Mr Tsymbaliuk had in fact gone straight to Ukraine's security services, and recorded all their interactions.
A few days before the fake assassination was due to take place, Mr Tsymbaliuk met his target - Mr Babchenko - for the first time at the Russian journalist's apartment.
"A [security service] operative introduced us to each other with the words 'say hello to your possible murderer'," Mr Tsymbaliuk says with a chuckle. "I told him: 'You don't get a chance every day to do a slap in the face of Putin'."
Then, on 29 May, the staged murder was unveiled, with Mr Tsymbaliuk going through the motions as if he was a real killer, in case he was being followed.
"I finished my soup, called a taxi and I went to kill Babchenko," he told the BBC correspondent with a smile.
"[At the apartment, Babchenko] was lying on the floor in a pool of blood waiting for the ambulance to arrive. I wished him good health and he asked that I not make him laugh."
With that brief exchange over, Mr Tsymbaliuk left to a safe house where he watched news of the murder emerge on social media.
Later that night, he sent a message to Mr Herman telling him that "the parasitic worm is dealt with" and in the early hours of the morning a reply came through that they should meet.
That meeting never happened as security agents moved in and detained Mr Herman as he made plans to leave the country. Shortly afterwards, Mr Babchenko stunned the world by being presented alive at a televised news conference.
Mr Herman has not denied plotting with Mr Tsymbaliuk but now says he was also working with Ukraine's SBU security services and knew all along that the assassination would be faked.
As yet Mr Herman and his legal team have produced no evidence to support that claim.
Russian writer and war correspondent Arkady Babchenko reportedly died of gunshot wounds to the back after he was attacked entering his apartment in Kyiv’s Dniprovskyi district on May 29.
On May 31, the Shevchenkivskyi district court of Kyiv imposed a 60-day pretrial detention without bail option against Borys Herman suspected of masterminding assassination attempt against Babchenko.
On June 1, Ukraine’s top prosecutor said that Babchenko’s staged assassination helped the investigation obtain a list of 47 individuals who could potentially be put a hit on by the Russian secret services.