"We were tied up, our hands behind our backs," said one man, in his early 30s.

Survivors allege they were packed into trucks in layers

"They packed us into the trucks, face down, and when the floor was filled they stacked others on top. In my truck there were four layers. I heard that some trucks were seven layers deep," he said.

These were the allegations of one of the survivors of Monday's protest in the southern Thai province of Narathiwat.

The man had been one of 1,300 loaded into army trucks by the military after the demonstration turned violent.

Their destination was military headquarters in Pattani, several hours north. But 78 men were dead before they arrived, having been suffocated or crushed to death.

I had gained access to the military headquarters with a delegation of Thai senators who had come from Bangkok to investigate the deaths.

We had been taken to the holding room where 200 men sat on the bare concrete floor. Many had fresh scars and bruises, but looked otherwise in good health.

The people responsible for this must be brought to justice, by legal means Kraisak Choonawan Senate foreign relations committee

As soon as the man had told me this, I was escorted outside by a soldier carrying an M16 rifle.

But the senators remained. As they came out they told more harrowing tales.

Senator Jermsak Bintong said one man said they were stacked inside the trucks like sardines.

"They cried out for help, but the soldier told them 'Now you know what it is like in hell'," the senator said.

He said he had been told that the detained men were beaten.

"They didn't dare to resist. If they did they were hit with rifle butts," he said.

"The people responsible for this must be brought to justice, by legal means," he continued, his anger quite visible.

Official story

The army, however, had a different story.

A presentation to the delegation showed knives, machetes and grenades that had been recovered from the scene of the protest, a police station in the town of Takbai.

First-hand accounts from some of the soldiers were shown who said they heard bullets being fired and saw guns in the crowd.

It is stomach-churning work for the men charged with cleaning the bodies

The commander of the fourth army that controls the southern provinces, Lt General Pisan Wattanawongkiri, admitted some mistakes had been made when he briefed the senators.

He said that some soldiers had become violent, but they were afraid.

The crowd had been set on causing trouble, he said.

He did not know who had given the order to pile the men into the trucks. His hunched shoulders and trembling voice suggested a man under great stress.

Just outside the main body of the camp lay the bodies of some of the dead.

Twenty corpses, their limbs twisted by rigor mortis and their flesh swollen in the hot weather awaited cleansing by a group of Muslim men. They must have had strong stomachs because the smell from 50 yards was overpowering.

As these images and stories filter out, Thailand's Prime Minister Thaksin Shinawatra will find it increasingly difficult to maintain his hard line on the violence in the south.

Many ordinary Thais now feel that the bloodshed is too great to be ignored. If Mr Thaksin cannot find a peaceful solution, it may well threaten his position.