Indeed, when the camera first records the Israeli shells tearing into the UN base at Qana, the other soldiers who appear in the film, most of them Norwegians in the UN's Force Mobile Reserve opposite Qana, seem unaware of its implications. One of them makes a joke, another looks gawkily into the camera even as it tapes the clouds of smoke obscuring Qana. The camera pans through barbed wire as more brown puffs of smoke emerge from the white-painted buildings of the UN's Fijian battalion headquarters.
Then UN officers can be seen at an observation post staring at Qana as the Israeli shells rain onto their colleagues and the helpless refugees across the valley. A group of Norwegian soldiers talk excitedly and the camera, its owner obviously growing aware of the gravity of the situation, moves in close-up towards Qana with a zoom lens until the videotape is filled with drifting smoke. Shortly afterwards the sound-track picks up the familiar buzzing sound of the Israeli "drone", final and irrefutable evidence that later Israeli denials were false - until the Israelis changed their story last night.
Refugees and UN officers had all talked of hearing the Israeli artillery "spotter" aircraft before and during the Israeli attack on the UN base. But here at last, in living colour, was the proof: distinct pictures of the small Israeli aircraft over Qana, the plane that the Israelis for two weeks claimed was never there.
One of the UN soldiers who saw the video being made says that neither he nor his colleagues understood in the first few seconds what was happening at Qana. "We know the Israelis are perfect in their accuracy. The previous day, when Katyushas had been fired a couple of miles away, we saw the Israeli return fire come back on the launch site with complete accuracy. We felt so safe about the Israeli artillery that we never went indoors when shells flew over.
"They knew we were here and so they never hit us. So we didn't even wear flak jackets when there were shell warnings. The Israelis knew what they were doing. And then we saw Qana and by the end, none of us believed it was an accident. Yes, the Israelis knew what they were doing. What do you think the 'drone' was for?"
A UN officer from a Nato nation who saw the videotape - a copy of which has been obtained by the Independent - before it was handed over to UN investigating General Frank van Kappen, was more emotional. "If the UN report is diluted to please the Israelis and the Americans, how is the UN going to live with it? How are we on the ground here supposed to pass by that mass grave [of more than 100 civilians in Qana] with a clear conscience?
"I and many others have risked our lives under constant Israeli shelling. We put up with their lies and the arrogance of their explanations. They blame us because we let unarmed Hizbollah men visit their families in our base. But back in 1984, Israeli soldiers were ambushed near my base and we let them in and protected them. Of course, the Israelis don't mention that now. But even if it means the end of my military career, I'll never say this was an accident. The Israelis knew they were firing at innocent people."
The UN have noted that an Israeli officer is also ensuring that his military career remains unblemished. For although the Israeli Prime Minister, Shimon Peres, denied knowing that more than 800 civilians were sheltering at the UN base at Qana on 18 April, Major General Moshe Yaalon, the Israeli army chief of intelligence, stated on the day of the massacre that the Israel Defence Forces knew of the civilian presence at Qana and that it was the Israeli army's Northern Command under General Amiram Levine - already reprimanded after his artillery fired into the village of Shaqra last year and killed a young Lebanese woman - which ignored the intelligence information.
"Yaalon knows something smells and he's keeping himself out of it," a European UN soldier said. "The Israeli investigation that Dan Harel [the brigadier commanding the Israeli Artillery Corp] carried out was cursory. He said they fired at the Katyushas and that only two rounds hit the UN base. This is bullshit. We know that at least 12 rounds hit the base, seven of them fitted with proximity fuses which explode the shells seven metres from the ground and are designed to kill the maximum number of people by inflicting amputation wounds."
Towards the end of the eight-minute videotape that has so transformed the UN's official investigation, the horror of Qana has been understood by the UN soldiers watching from the neighbouring hillside and by the amateur military cameraman. Just after he films the drone, he focuses the camera on a fire that is raging in the heart of the UN compound, the Fijian battalion conference room that was home to dozens of Lebanese refugees.
The flames burn white and red in the centre of the frame - the Israeli pilotless drone spotter-plane can still be heard on the sound-track - and then a pall of black smoke rises from the building in which the Lebanese civilians are being burned alive.
On the videotape, the soldier is now recording the UN radio. An Irish voice says: "Fijibatt headquarters is still under shelling." One of the UN soldiers who stood close to the cameraman was to tell me later that in one observation post a colleague could hear - a mile away across the valley at Qana - "a sort of chorus of screaming".
A set of still photographs of the shelling, which the Independent has also obtained, shows only one shell falling outside the compound, in the opposite direction to the Katyusha launch site at which the Israelis claim they were firing.
The last sequences of the tape are taken as the cameraman and his colleagues in the UN's Force Mobile Reserve, including Irish, Norwegian and Fijian soldiers, race in armoured vehicles to the Qana base amid a convoy of ambulances. In confusion, a medevac team drop an empty stretcher on the ground and then, drip-feed held over a figure on another stretcher, haul a wounded refugee into an ambulance. The camera moves to a hill where a white-painted UN helicopter with wounded on board is preparing to take off. On the ground in front of it stands an injured Lebanese woman, a bandage round her head, holding two small children by their hands.
As the rotor blades swish the air above them, the Italian pilot climbs out of the plane, shooing them away, moving his arms back and forth, ordering them back from the helicopter.
With a kind of desolation, the woman, in a blue dress, half her face in bandages, leads the two children down the hill from the helicopter, accompanied by two shocked Fijian UN soldiers.
Leading article, page 14