He led a journalists' strike against the takeover of the newspaper by United Malays National Organisation (UMNO). Also known as Pak Said he was detained by the government of Singapore and subsequently held for 17 years without trial. Allegations against him included being a "Communist". He now holds the distinction of being the second longest-serving political detainee in Singapore after Chia Thye Poh.
A documentary made by Film maker Martyn See about his 17 years as a political prisoner in Singapore was banned by the Board of Film Censors under the Films Act, which prohibit its procession and distribution.
In the documentary, Zahari recounts the events that follows his election as chairman of Parti Rakyat Singapura on the night before Operation Coldstore. He details his subsequent detention where he was kept in solitary confinement for long period in poor condition and explicitly threatened with death if he did not choose to confess his alleged crimes and cooperate with the authority. Part of the film shows Zahari conversing with the interviewer in fluent Mandarin, which he was taught during his forced detention without trial by fellow Chinese educated detainees, who were amongst majority.
In a Singapore government media release highlighting the ban, it was stated that the documentary in question, "gives a distorted and misleading portrayal of Said Zahari's arrest and detention under the Internal Security Act in 1963