Judge Cicit Sutiarso did not say whether the court believed that Pollycarpus Priyanto was acting on someone else's orders when he placed a lethal dose of arsenic in food served to Munir Thalib, on a Garuda airlines flight to Amsterdam on 7 September 2004.
Critics have said that Priyanto, a pilot who was off duty on that flight, was a scapegoat and that the masterminds, possibly members of the State Intelligence Agency, had escaped punishment.
The judge told a packed court on Tuesday: "The accused's motivation to kill Munir was because he was a vocal critic of the government and the Indonesian military."
The trial is seen as a key test of whether the government of Susilo Bambang Yudhoyono, the president, can break with the traditions of the Suharto government, when state sponsored killings were common and the legal system was perceived as
bound to the ruling elite.