Zhao, a supporter of democratic reform in mainland China, was jailed after the massacre and then placed under house arrest for the simple reason that he sympathised with the students.
To this day official Beijing describes the students and workers who were slaughtered on that fateful night as dangerous counterrevolutionaries.
Across the country the wound is still open as the authorities continue to refuse to discuss the events, censoring and jailing anyone who dares to talk about it or seek the truth about what actually happened.
In his memoirs Zhao notes that students had come to the square to speak out against corruption, and demand democratic reforms, not to overthrow the system of government.
However, the situation precipitated when a controversial editorial was published on 26 April in the Chinese Communist Party mouthpiece, the People's Daily, labelling the students as “anti-party, anti- socialist turmoil”.
For Zhao the editorial paraphrased statements made by then paramount leader Deng Xiaoping in a private discussion, in which he had taken a position against the demonstrators. This led protesters to continue their demonstrations and prevented any dialogue, making a violent showdown almost inevitable.
“The crux of the issue was Deng Xiaoping himself,” Zhao writes. “If Deng refused to relax his position, then there was no way for me to change the attitude of the two hardliners, Li Peng and Yao Yilin.”
Ultimately though, the final responsibility was with the paramount leader.
“Deng Xiaoping had always tended to prefer tough measures when dealing with student demonstrations because he believed that demonstrations undermine stability.” He “had always stood out among the party elders as the one who emphasised the means of dictatorship” and “often reminded people about its usefulness. Every time he mentioned stability, he also emphasised dictatorship.”
The memoirs are based on 30 hours of recorded tapes that were smuggled out of China for the book, and edited in the strictest secrecy by friends and aides of the late leader.
Mr Zhao's former secretary, Bao Tong, said he was behind the scheme to publish his former boss's memoirs.
Mr Bao spent seven years in prison because of his involvement in the Tiananmen crackdown and is still under house arrest in Beijing.
He said that he edited both the Chinese and the English edition (with the assistance of his son Bao Pu), hoping that it “will cause party members to reflect deeply.”
In his revelations, Zhao Ziyang calls on the Party to review its judgement of the protests and massacre and adopt democratic reforms including multiparty politics, a free press and an independent judiciary.
In mainland China the release of Zhao’s book has been received so far with an embarrassing silence.
No official comments have been.