Crossing no man’s land from the last Syrian government checkpoint into the centre of Houla is an edgy business. The UN officer commanding the patrol advised us: “Keep at least 50 yards between you and the vehicle in front. If the shooting starts the plan is to turn round and get the f*** out. Remember again you’re on your own here – good luck.”

Warning: You may find some of the content in Alex Thomson’s accompanying video distressing.

So it’s a straight run for a mile or so to the next roundabout where a dead horse bloated and rotting in the middle of the road is the point where you know you have crossed the line. This does not mean safety from either snipers or shelling.

“They’re under a hell of lot of pressure to let us in this morning,” the same UN officer advised us speaking on condition of anonymity, “after the Kofi Annan visit yesterday.”

Indeed, all the way from Homs across the line into rebel held Houla, we heard not a single shot, nor any incoming artillery.

At the first signs of human life in rebel territory loud shouts of “freedom, freedom, freedom”, v-signs for victory and by the time we had managed to get out of our van we were completely mobbed by people shouting and crying in a mixture of relief, shock and anger.

At once we were pulled physically from house to house by people desperate to get their story to the outside world. Within minutes we meet 25-year-old Younis, lying in a room with two gunshot wounds in his torso. He’s telling us, weakly, how he was trying to help an 11-year-old boy on Friday when he was injured. The boy was shot dead.

A 15-year-old girl lies on another bed not 10 yards away describing how she witnessed the Shabiya militia crouching behind a window as she tried to flee. She too was shot.

Abdul Bari, 30, describes how he came by blast wounds during the protest after prayers on Friday.

Whether we like it or not we were pretty much dragged onto the streets again. On one hand an 8-year old boy shot in the arm, next to him a man showing us video on his telephone of two children, their throats slit so deeply they are virtually decapitated.

Another man suddenly approaches, educated with good English. He has gone through the emotions to reach cold, measured anger.

Over the next three hours I will deliberately ask him the same question to see if his story alters in any detail. It does not. He is willing to be interviewed and identified on camera. But to protect him we do not do this. Channel 4 News knows his name and full identity.

He describes in detail the world has not heard before what happened on Friday. He matters because over the next five hours we spend in Houla, scores of people will corroborate his story in various details.

He describes how there was intense shelling of the ground for several hours. After that the Shabiya – armed militia – entered the town from the southern to south western direction. He says there were around 100 of them dressed in military uniforms. They approached Dam Road which connects the large reservoir to the Houla villages. He says – and all agree – these men were Shia and Alawite who had come from specific Shia/Alawite villages to the south and west of Houla.

 The searing grief of Houlas survivors

He names several villages and later we are taken to a rooftop where we can see those villages from the overwhelmingly Sunni town of Houla.

Two names come up time and again – Kabu and Felleh. They are so close, not more than two or three mile as the most. He goes on describing how the killers had written Shia slogans on their foreheads as they went house to house searching out and slaughtering Sunni families.

He says to us: “They have slaughtered us, they have killed us. When this is all over we will be victorious. And we will go there. And we will find them out and we will slaughter them and we will kill them. We will kill their men, women and children as they killed our men, women and children.”

Time again we are told there are many bodies still to be recovered.

On Sunday, I saw myself two bodies the UN is unaware of. At the mass grave containing at least 100 bodies – mostly women and children -they have been careful to leave a large open trench to take more corpses which will be simply wrapped in cloth – coffins are impossible. They do not even have running water or electricity in this town. Let alone luxuries like coffins.

The UN clearly agrees with their assessment. This afternoon part of their mission was the retrieval of more corpses but the difficulty is that they lie in areas close to Syrian army checkpoints considered too dangerous to reach.

There is an overwhelming and searing grief. What can you say? What can you do? What can you offer an elderly man, Abdul Hamad, who knows not only that his daughter was killed but that her throat was hacked with a knife, it seems, wielded by men who live just a few miles distant.

You can follow Alex on Twitter @alextomo