Le Tan Gia, 46, was arrested by the police on Friday to be investigated for violating food safety regulations.
Gia worked as a bartender at a restaurant in Hoi An. On Dec. 24 last year, he mixed antiseptic alcohol 70%, which is used for disinfection, with water, lemon zest and sugar to make two bottles of Limoncello.
The mixture was later provided to Ottson Greta Marie, 33, a British woman, and Els Arno Quinton, 36, a South African man, authorities said. The two were later found dead inside a villa room in Cam Thanh Commune.
The police found used alcohol bottles at the scene, noting that there was no sign of physical trauma on the bodies.
Both tourists died of methanol poisoning, authorities concluded.