More than 23 hours a day in a Chinese prison cell. Virtually no access to sunlight or medical care or exercise. Those are the conditions 76-year-old Jimmy Lai has endured day after day, year after year, since he was arrested under China’s national security law nearly four years ago, according to his international legal team.

That legal team submitted an urgent appeal to the United Nations last week on behalf of Hong Kong’s most famous freedom fighter, alleging that China’s detainment of the media mogul is torture.