Anthony Deutsch, Jakarta – Human rights groups on Sunday criticized a Supreme Court decision overturning the 14-year prison sentence of a man convicted of killing Indonesia's most prominent activist.

Munir Said Thalib, a human rights lawyer who was threatened in the late 1990s after revealing abuses by the Indonesian military, died of arsenic poisoning in September 2004 on a flight from Jakarta to Amsterdam.

The Supreme Court on Tuesday said it had seen insufficient evidence to back up an earlier decision by a lower tribunal that an off-duty pilot, Pollycarpus Budihari Priyanto, had laced Munir's food with poison.

The acquittal has angered many in Indonesia, where the case was seen as a test for a legal system still plagued by corruption after nearly three decades under former dictator Suharto. His regime, toppled by a popular uprising in 1998, was known for the widespread imprisonment and killing of political opponents.

"The failure to secure a conviction for Munir's murder is a huge blow for human rights protection and the reform process supposedly under way in Indonesia," Brad Adams, Asia director for the New York-based rights group Human Rights Watch, said in a recent statement.

Munir's wife, Suciwati, who like many Indonesians goes by a single name, maintains the murder was the result of a conspiracy by military intelligence members who wanted to get back at Munir for his activism. She has said the key to Munir's case lies in a trove of telephone taps between a high-ranking Indonesian general and the pilot, which the intelligence service refuses to make public.

That theory was supported by Asmara Nababan, an Indonesian rights activist and member of the fact-finding team established by the government last year to probe the case. The team concluded that Priyanto had had contact with an agent from Indonesia's intelligence agency, information which never surfaced in court.

Nababan said Sunday that if Indonesian President Susilo Bambang Yudhoyono "had given full support, I believe the murderer, the executioner and the mastermind could be punished by now."

The president's spokesman told reporters after the court's decision was announced that Yudhoyono has ordered police to "improve and heighten their investigation."

The criticism comes at an awkward time for Yudhoyono, a leading contender for this year's Nobel Peace Prize for helping to end a bloody war in Indonesia's Aceh province.

Experts and bookmakers are predicting the Norwegian committee that awards the prize will honor the Aug. 15, 2005, peace agreement between the Indonesian government and Aceh separatist rebels which ended 29 years of fighting that left 15,000 people dead. Former Finnish President Martti Ahtisaari, the mediator of the accord, is considered the favorite, followed by Yudhoyono.

"As an Indonesian citizen I am proud he was nominated," Munir's wife told reporters after the court's decision, "but as a victim I feel he should never get the prize, unless he resolves this murder."

[Associated Press writer Niniek Karmini contributed to this report.]