Three former Guatemalan army officers have gone on trial charged with masterminding the murder of an anthropologist 12 years ago.

Myrna Mack was stabbed to death outside her office in Guatemala City in 1990 during the country's civil war.

A retired general, Edgar Godoy, and two former colonels, Juan Oliva and Juan Valencia, deny the charges and the authorities said at the time that the killing was committed during a robbery.

Civil war

Ended in 1996 after 36 years Some 200,000 people killed or missing

But Ms Mack's family say she was targeted after uncovering evidence that the army was mounting a campaign against peasants suspected of supporting left-wing rebels.

Ms Mack's sister Helen has campaigned vigorously for the killers to be brought to justice.

"The army thought that the farmers displaced [by the civil war] were working with the guerrillas, and that my sister's humanitarian work with the farmers would interfere with the counter-insurgency campaign," she said.

Helen Mack and her lawyer Romero Robert were both granted protection from the government after they received numerous death threats.

Rare trial

The case is thought to be only the second time Guatemalan military leaders have been put on trial for wartime crimes.

In June 2001, the same court in Guatemala City sentenced three soldiers and a priest to lengthy prison terms for their roles in the assassination of Bishop Juan Gerardi.

Few people have been charged for war crimes

Sergeant Major Obdulio Villaneuva, former Colonel Disrael Estrada Lima and Captain Byron Lima Oliva all received 30 years each while Mario Orantes, a priest who had worked with the bishop, received 20 years.

All four men have appealed against their sentences.

Like Myrna Mack, Bishop Gerardi was a human rights advocate.

He was bludgeoned to death in April 1998, just two days after he produced a report that blamed the army for many of the assassinations during the 36-year civil war.