‘Prisoners killed each other’s kittens. So now they’re forbidden inside’: Vladimir Karamazov’s best photograph

• Belene prison, in northern Bulgaria on the border with Romania, is the most heavily guarded facility of its type in my country.
• It is on an island, so escape is near impossible, and has the largest number of people serving life sentences for murder in any Bulgarian prison.
• This image describes a sad, terrible story.