At first, the shaky video seems to show a group of people walking together toward the camera along a dirt road somewhere in sub-Saharan Africa. As the group moves forward, it quickly becomes clear it is made up mostly of armed men and they are roughly pushing forward two women with children.

The video began circulating on various social media sites in July, and ends in horror, as a young girl of about six, and the women, one with an infant strapped into a sling on her back, are blindfolded, told to sit and executed. They are shot as many as 22 times.

"We were appalled by the video," said Daniel Adamson, a producer with BBC Africa Eye, one of those on a reporting team who set out to determine where the atrocity had happened.

Adamson spoke with CBC News for this week's episode of The Investigators with Diana Swain.

The BBC used some of the newest techniques in journalism to unlock the details of a brutal viral video. Diana talks to Daniel Adamson, a producer with BBC’s Africa Eye, who led the investigation. Watch The Investigators with Diana Swain Thursdays at 7:00 pm on CBC Television; Saturdays at 9:30 pm ET and Sundays at 5:30 pm ET on CBC News Network. 4:31

Adamson and his colleagues turned to the process of video verification, an emerging journalism technique, to find the truth.

"These open source techniques are very valuable for that."

Using private communications channels on Twitter and Slack, Adamson says the team reached out to the wider online community to help identify specific references in the video.

Official denials

Amnesty International and many commenters on social media who saw the video believed the armed men were soldiers in Cameroon's government. But the country's Minister of Communications, Issa Tchiroma Bakary angrily denied that, insisting the video was "nothing but an unfortunate attempt to distort the facts and intoxicate the public."

Cameroon's government dismissed the video as "fake news," and others supporting the government suggested the atrocity had likely taken place in another country, Mali.

Google Earth made it possible for journalists to identify specific buildings in the village where the execution took place. (BBC Africa Eye)

Adamson said various people responded to the BBC's request to help scrutinize the video for specific clues to who the men were, and where it happened.

"These are people who are specialized in, for example, geolocation, or some of them are specialized in weapons analysis or in tracking vehicles, planes and boats," he said.

For example, a ridge-line that appears on the horizon in the background, was matched using Google Earth, to a mountain-range in the north of Cameroon.

'Real rigour'

Even the shadows thrown by the soldiers as they walk, helped pinpoint the time of year the video was made.

Taken together with other details, the team was able to determine the video had indeed been taken in the north of the country in the spring of 2015, near the Nigerian border where troops from Cameroon had been fighting the militant group, Boko Haram. In the video, the soldiers are heard accusing the women of supporting the rebel group before they are shot.

Journalists used Google Earth to establish the location of a ridge in the video in order to understand where the killing took place. (BBC Africa Eye)

Adamson say this kind of approach by journalists to finding the truth of an event is becoming more important.

"Everybody from rural Cameroon to Syria is carrying a mobile phone camera in their pocket. And there are now thousands of incidents, including serious abuses, and even atrocities like this, which are being uploaded every day to social media. So, in that context it's so important that the media has ways to analyze and verify these videos with real rigorr."

Beyond that, Adamson says the meticulous way the BBC showed its work, both in a documentary and a frame by frame Twitter thread that's now been retweeted more than 50,000 times, helps show the public how the analysis was done.

THREAD<br><br>In July 2018, a horrifying video began to circulate on social media. <br><br>2 women & 2 young children are led away by a group of soldiers. They are blindfolded, forced to the ground, and shot 22 times. <a href="https://twitter.com/hashtag/BBCAfricaEye?src=hash&ref_src=twsrc%5Etfw">#BBCAfricaEye</a> investigated this atrocity. This is what we found... <a href="https://t.co/oFEYnTLT6z">pic.twitter.com/oFEYnTLT6z</a> —@BBCAfrica

"Increasingly, audiences do not want to take findings on trust, they want to see with their own eyes, how you arrived at a certain conclusion."

Cameroon's government has since arrested and charged seven of its own soldiers with the crime.

Also this week on The Investigators with Diana Swain, Global News reporter Carolyn Jarvis talks about a joint investigation into illegal drug sales by some Ontario pharmacists, and CBC producer Josh Bloch talks about his podcast: Uncover: Escaping NXIVM and what it was like to chronicle his friend's escape from a cult.