On April 12, 2022, Zelensky announced that the Security Service had detained Viktor Medvedchuk, the leader of the Opposition Platform for Life party, the second most represented in the Ukrainian parliament.

On March 20, contrary to the Constitution of Ukraine, the president by his decree banned the activity of this party, along with the activities of some other, mostly leftist, parties. After that, the Opposition Platform ceased its activities.

Before that, Viktor Medvedchuk had been under house arrest for about 8 months on charges of "high treason" and "illegal trade" in coal with the republics of Donbass.

On February 27, three days after the outbreak of hostilities, there were reports from his lawyer that he had warned the Prosecutor General's Office and the Security Service of Ukraine that he was receiving threats from radical nationalist groups and, in agreement with them, had taken away his place of stay due to a real danger for life.

At the same time, Medvedchuk undertook to fulfill all the procedural duties assigned to him.

On the same day, Anton Gerashchenko, an adviser to the Minister of Internal Affairs, said that Medvedchuk had "escaped" from house arrest. But at the same time, he said that the unnamed judge decided to remove the control bracelet from Medvedchuk. Gerashchenko also threatened this judge with reprisals from the ultra-right "territorial defense".
https://www.ukrinform.ua/rubric-politics/3414835-medvedcuk-vtik-zpid-domasnogo-arestu-mvs.html

On March 18, the Lviv court, in the absence of Medvedchuk, decided to keep him in custody: https://novoeizdanie.com/sud-zaochno-arestoval-viktora-medvedchuka/

Where Viktor Medvedchuk stayed from February 27 to April 12 is unknown.

There are doubts about the version of the Kiev authorities that Medvedchuk dressed in a military uniform and wanted to flee the country. In the presented photo, we see that he is dressed in absolutely clean shoes and a uniform that does not fit him.

In addition, there is a mark on Medvedchuk's head, which may indicate that physical force was applied to him.

Zelensky announced that he was ready to exchange Medvedchuk for captured Ukrainian soldiers. But there is no legal basis for the "exchange" of a citizen who is under investigation.

Thus, Zelensky actually confirmed that there is an "exchange fund" that is being filled with detained journalists, public and political figures.

And that Medvedchuk is being held hostage by him.

There is a version that Zelensky wants to exchange Medvedchuk for officers from NATO countries who lead the encircled units of the Ukrainian army in Mariupol. But Putin is unlikely to agree to this.

The second version: by showing the detained Medvedchuk, Zelensky wants to reduce the negative information effect for him from the event that happened a few hours before. In Mariupol, more than a thousand Ukrainian marines surrendered to Russian soldiers.