Indonesia's state intelligence agency asked the country's national airline Garuda to transfer one of its pilots to its corporate security unit shortly before a mid-air murder, a court was told.

High-profile activist Munir Said Thalib, 38, was poisoned with arsenic during a Garuda flight to Amsterdam in September 2004. He had made some enemies while exposing human rights abuses in Papua and East Timor.

Prosecutors at a hearing in Central Jakarta District Court have alleged the powerful state intelligence agency BIN played a role in the murder.

Hundreds of people on Wednesday crammed into Central Jakarta District Court, which has reopened the case against off-duty Garuda pilot Pollycarpus Budhiari Priyanto.

Garuda Executive Director Indra Setiawan told the court he received a letter from BIN in 2004 asking that Pollycarpus, a pilot, be made a member of Garuda's corporate security unit. Setiawan told the court that Pollycarpus had asked to meet him at a Jakarta hotel.

"After that, Pollycarpus handed me an envelope which had a letter in it," he said. "I opened it and there was letterhead of the national intelligence agency. The letter was not long. The essence of it was that, as a vital and strategic company, there was a need to enhance the security and therefore to assign Pollycarpus to the corporate security unit of the company."

Pollycarpus was originally convicted and jailed for 14 years over the murder of the activist but the Indonesian Supreme Court last year overturned the conviction on appeal, citing a lack of evidence. The case was reopened after Indonesia's Attorney General's Office recently submitted a request for a review of the case.

Security was tight at the court, with an anti-riot vehicle parked in front of the building and heavily armed riot-police and bomb squad officers on guard. Munir's wife Suciwati was present for the hearing.

Former BIN spy agent Raden Muhammad Patma, aka Ucok, also testified, but evaded repeated questions about the national intelligence agency. Prosecutors had alleged in their written dossier that BIN had asked Ucok to kill Munir, but he denied it on Wednesday. The hearing continues.