Abijeet Nath and Nilotpal Das were driving back from a visit to a waterfall in the Indian province of Assam earlier this month when they stopped in a village to ask for directions. The two men were pulled out of their car and beaten to death by a mob who accused them of stealing children.
"The villagers got suspicious of the strangers as for the last three or four days messages were going around on WhatsApp, as well as through word of mouth, about child lifters roaming the area," Mukesh Agrawal, a local police officer said.
Indian police have linked dozens of murders and serious assaults to rumours spread on the messaging service in recent months.
In Brazil, WhatsApp has been blamed for a yellow fever outbreak after being used to spread anti-vaccine videos and audio messages. In Kenya, WhatsApp group admins have been described as a major source of politically motivated fake news during recent elections. And there are signs that the messaging service is being used as a conduit for misinformation in the UK.
New analysis by the University of Oxford's Reuters Institute found that consumers around the world are reading less news on Facebook and are increasingly turning to WhatsApp - which has 1.5 billion active users worldwide - to share and discuss news stories.
"In some sense it's not that dissimilar to ordinary conversations but what makes it different is the speed with which these things can spread," said Nic Newman, who co-wrote the report. "The reasons why people are moving to these spaces is because they get more privacy. If you're in an authoritarian regime you can use it to talk safely about politics - but it can also be used for nefarious means."
Newman said WhatsApp's privacy settings make it difficult to ascertain the scale of misinformation on the service: "It's very early days but I've got a hunch this is going to become a much bigger story."
WhatsApp lets users send messages, links, pictures and videos to other users. Unlike Facebook, Twitter and Instagram, it has no algorithm deciding which content is shown to users, no ability for outside companies to buy adverts and discussion happens within private groups.
This should in theory make it harder to manipulate and there is little chance of a large-scale Cambridge Analytica-style scandal. But its use of end-to-end encryption means that no one - not even the creators of the app - can intercept and monitor messages between users.
This has angered government officials around the world - including in Britain - who want to have the ability to monitor potentially illegal behaviour. But it also makes it near-impossible for WhatsApp to intercept misinformation being shared.
Even measuring how a story spreads on WhatsApp, which is owned by Facebook but run as an independent business, is nearly impossible.
"People don't want to put themselves in the public domain by putting something publicly on Facebook and Twitter, but there's still need for humans to gossip and share communication," said Camilla Wright, who has run the Popbitch email newsletter since 2000 and tracked the evolution ofonline gossip.
"People are sending things to each other on email again and on WhatsApp," she explained, drawing parallels with the round-robin letters and private forums that existed before Facebook and Twitter. "It's much more in tune in with how humans have evolved to gossip because it feels like you're telling people on a one-to-one level. The closed WhatsApp group is the modern water cooler or school gate."
The sense that news is being provided in secret by a friend - who got it from their friend, who claims to have got it from their friend, who claims to be in the know - is part of the appeal and only adds to the credibility of rumours.
British users got a taste for this recently when a rumour spread that David and Victoria Beckham were about to announce their divorce. Much of the speculation, which was strongly denied by the Beckhams, came from a series of screengrabbed messages that spread through WhatsApp, allegedly from people in the PR industry who had the inside track.
"My sister's friends sister works in a PR agency in London and apparently they are pulling an all nighter tonight in advance," claimed one of the widely distributed messages, with no supporting evidence. Another featured a now-suspended junior employee at London PR firm the Communications Store who used her work email to tell her family members that the "news is being broken in the papers today/tomorrow".
The agency has since made it clear that she was not the original source for the rumour and was only passing on gossip she had heard on Twitter. But taken together, the two images appeared to provide double-sourcing from people who could conceivably know the real story. Within hours they had been widely shared around the world, in an impossible-to-track manner.
For its part the messaging service is aware that it is dealing with a growing problem, which has already prompted the growth of fact-checking services in countries such as Mexico.
A WhatsApp spokesperson said some people used the app to spread harmful misinformation. "We've made it easy to block a phone number with just one tap - and are constantly evolving our tools to block automated content. We're working to give people more control over private groups, which remain strictly limited in size. We're also stepping up our education efforts so that people know about our safety features, as well as how to spot fake news and hoaxes."
But veterans of the online news business see the private nature of the service as being perfect for unmediated gossip. "People feel much more comfortable sharing important things through WhatsApp," said Wright. "It's that feeling of being in on a secret that people love."