Investigating officer Akhilesh Pratap Singh told CNN that the dolphin’s carcass was found at the Sharda Channel dike in the Pratapgarh district on December 31.
On Thursday, three people allegedly seen in the video were arrested, police said. Nine people – also seen in the video – are still on the run, according to Singh.
The video shows a group of men with sticks and an ax beating the dolphin to death. Some laughed when the dolphin’s nearly lifeless body was pulled by the fin in the shallow water.
Forestry officer Varun Singh, who was part of the initial investigation, told CNN that the dolphin was an adult dolphin from the Ganges River.
The Ganges river dolphin “has been present in tens of thousands of people”, but has now “declined abysmally” for a population of less than 1,800 in the past century, according to the World Wildlife Fund (WWF) India.
The rare freshwater dolphin is essentially blind and is known locally as “susu”, a reference to the noise it makes when breathing, according to WWF.
When hunting, the dolphin emits ultrasonic sounds that bounce off fish and other prey, allowing them to visualize an image in their mind.
The female dolphins of the Ganges river give birth once every two or three years to just one calf, according to the WWF.