Rights groups worry the case could hamper media coverage of corruption
Two Vietnamese journalists who helped expose state corruption have gone on trial, in a case that has put Vietnam's media freedoms under scrutiny.
The two reporters, from the well-known newspapers Tuoi Tre and Thanh Nien, are accused of "abusing freedom and democratic rights".
They allegedly fabricated unspecified "sensitive information" while covering a high-profile corruption case.
It is not known how the accused pleaded when they appeared in court in Hanoi.
Two former high-ranking police officials have also been taken to court for allegedly leaking unauthorised information to the media.
The so-called PMU-18 scandal, which broke in early 2006, was named after a unit of the Ministry of Transport.
Officials were found to have stolen development funds meant for roads and bridges, betting much of the money on European football.
The scandal led to the arrest of a number of high-ranking officials and the departure of the then minister of transport Dao Dinh Binh.
Journalists Nguyen Van Hai, 33, and Nguyen Viet Chien, 56, were arrested last May and have been held since. Each wrote more than 50 news and feature stories on the case.
If found guilty, they could face up to seven years in jail.
The same jail sentence may apply to Maj Gen Pham Xuan Quac and Senior Lt Col Dinh Van Huynh, the two policemen accused of deliberately disclosing investigative secrets.
Ahead of one of the most talked-about trials in Vietnam in recent years, the domestic press, paradoxically, stayed silent.
It is believed that the ideological department of the Communist Party, which maintains close control over the media, instructed reporters covering the two-day trial to report "only facts and no commentary".
A reporter in Hanoi, who wanted to remain anonymous, said: "They want to make sure that the press write about it as an ordinary trial and not one with any political implications."
The case originally examined football betting allegations at PMU-18, but gathered political steam after the arrest in April 2006 of vice minister Nguyen Viet Tien.
Mr Tien was once in charge of PMU-18 and at the time of the arrest was considered a ministerial hopeful.
The case brought prolific media attention to his wrong-doings as well as his "immoral and decadent" lifestyle.
Another rising star of the regime, Maj Gen Cao Ngoc Oanh, lost his position as head of investigative police after newspapers named him as having personal contacts with someone implicated in the scandal.
But the case took an unexpected turn last spring when the authorities cleared the vice minister of corruption charges.
The spotlight then turned on the media reportage, soon deemed by the authorities to have been "erroneous" and "harmful".
Fear for coverage
The subsequent arrest and prosecution of the two reporters has stirred up a storm, as Tuoi Tre and Thanh Nien are among the largest newspapers in the country.
Foreign governments have expressed concern and rights organisations have repeatedly called for the release of Mr Hai and Mr Chien.
They express fear that their plight will deter newspapers from reporting on corruption cases in future.