Being knowledgeable ≠ being clean
What do corrupt officials do when they end up behind bars? Maybe write books if the conditions are right. Quite a number of them have had their books published even while serving their terms.
Zhang Erjiang, former Party secretary of the city of Tianmen in Hubei province, who was sentenced to 15 years in jail for embezzling public money and accepting bribes in 2002, has had four books published since then. Zhou Jiugeng, a former bureau chief who was notorious for smoking cigarettes of a prohibitively expensive brand and was sentenced to 11 years, is reported to be progressing well with his novel in jail.
Apart from one former official who has written a book about how high the cost is for being corrupt, none has written anything to suggest they repent of the crimes they committed in their positions. The four books by Zhang Erjiang are about ancient Chinese literature; some have written novels and others on a subject they are familiar with.