A cellphone left behind in a taxi in Fiji has revealed shocking content - a graphic video showing what looks like a summary execution at sea of four men in the water by a number of gunmen in ships.

The 6-minute-58-second video shows one man bobbing in the water and raising his arms in surrender, before he is shot in the head, his blood later staining the blue water he was floating in. The other men, who seemed to be holding onto pieces of wreckage from an overturned wooden boat, were surrounded by several large tuna longliners, according to The New York Times.

At least 40 rounds were fired at the unarmed men floating in the sea as they were picked off one-by-one. As each of the men in the water was methodically killed, some crew members appear on deck, laughing among themselves, even posing for selfies.

At least four ships were visible in the video found on the cellphone, showing that there were dozens of witnesses to the murders. However, the killings were never reported to the authorities. Law enforcement officials only found out about the incident after the footage was found in the cellphone and the video was later uploaded on the internet, reports NDTV.

The identities of the victims remain unknown to this day, and none of the bodies of the men have been uncovered. Taiwanese fishing authorities, who were able to determine that one of the boats in the video was a fishing boat from the country, believe that the executions were the result of a failed pirate attack.

However, Klaus Luhta, a lawyer with the International Organization of Masters, Mates & Pilots, a seafarers' union, believes there may be more to the story than what the Taiwanese authorities would like to believe.

"Summary execution, vigilantism, overzealous defense, call it what you will," he said, adding "This boils down just the same to a case of murder at sea and a question of why it's allowed to happen."

Execution videos have become quite commonplace lately, especially with the videos that the Islamic State has been using as propaganda, an issue which is covered by this HNGN article.

Watch a part of the execution video here: