Police have concluded their investigation into the fatal shooting of a taxi driver on Koh Samui after arresting all 12 suspects, ruling out any links to organised crime on the tourist island.

Police said on Wednesday the killing stemmed from a long-running personal dispute between rival groups of taxi drivers and was not connected to any mafia network, despite speculation on social media.

The victim, 30-year-old Sikkharin Phromcharoen, was shot six times on May 24 in Bo Phut district. The attack took place in a public area in front of residents and tourists. He later died in hospital.

Investigators found tensions had existed for some time between the victim and a group led by another taxi driver, Sahaphol (surname withheld). On the day of the shooting, Sikkharin had just dropped off a foreign passenger when he met the group. An argument ensued before Prakasit allegedly opened fire.

Police used CCTV footage and other evidence to identify the suspects and obtain arrest warrants for all 12 individuals. The final suspect, Thawatchai, was arrested on Monday. 

The Koh Samui Court has denied bail requests.