You've learned he doesn't have the class or self control to be in house arrest. So he has to be imprisoned.
You either
A. Put him on a flight to fuckin anywhere else (you can even use him as leverage, or as a "good will gesture" by making him convey a message of gratitude to his captors)
B. Let him languish in a prison until he dies because you're mad that you've lost hundreds of thousands of men, and are on the back foot, to the point you're now mobilizing your country's women, and proposing children be put to work.
Enter chilean journalists that constantly calls your government an illegitimate regime ruled by a dictator. That takes videos and explains how certain areas are defended and posts them online. He is giving valuable propaganda for your enemy, potentially demoralizing your fellow fighters and potentially moralizing your enemy fighters. He seems fairly clueless, so you decide to clue him in. You rough him up a bit, imprison him a bit. Expose the enemy propaganda for being liars by making them believe he's dead and then after they reported his death, releasing him in house arrest.
How fucking dumb is Ukraine's desperate propaganda now?
The government suspended elections.
The government conscripts soldiers and gives them 3 weeks of training, with little to no practical training.
The same government is asking other nations to deport Ukrainian citizens back Ukraine to fight and die.
This desperate government can't properly use a prisoner for leverage?
Russia literally got one of their old high value assets out of a US prison for a fuckin basketball player who was caught with some weed.
Biden unfroze 6 billion dollars worth of assets and gave clemency for five Iranians in exchange for five Americans.
Trump brought home 58 hostages in his time as President through his own negotiations.

And we
know that this American government is incompetent, and Ukraine wants money from them.
Afghanistan:
Lord Miles (War Tourist) was released to the UK.
Jere Van Dyk (Journalist) was released.
Kevin Cornwall (UN worker) was released.
And this is an Islamic theocracy giving up civilians of states (The UK/US) that literally declared war, labeled the Taliban terrorists, and tried to create their own proxy government while killing thousands of Taliban.
Afghanistan's Taliban has better PR than Ukraine.
What is Ukraine going to get out of letting a man die of pneumonia in their custody? You think that Gonzalo was giving away "True and Honest" intel to the Russians on Ukrainian positions? As if Russia doesn't have satellites and drones that can look at every single checkpoint on the map?
The SBU knew about him the whole time LMAO. But this organization is so fucking up its own ass they can't see outside of their own perspective.
Even if he's not actually dead, and Ukraine is "merely pretending" he is to somehow "get a win" which sounds like utter bullshit, they're calling attention to themselves in the dumbest way possible, by shining a light on how they treat their prisoners.
Fuckin hell does no one understand statecraft anymore?