Rico Adeva, 39, was shot in the head and chest, killing him on the spot. His wife, Nenette, was unharmed.
Nenette said they were on their way back to their house from the market when the tragedy happened.
She said they had just crossed the Imbang River when the three men rushed toward them from the sugarcane field in Hacienda del Fuego 2 in Barangay Dos Hermanas.
The three men, brandishing short firearms, ordered her to kneel down and bow her head while they shot her husband.
She said she was able to run away and sought the help of their neighbors.
The three men fled but returned minutes later and took Adevas money reportedly amounting to P200.
Some residents told police investigators that they noticed three men loitering at the crime scene a week before the shooting, but did not notice anything unusual, thinking that they were attending a wake nearby.
Superintendent Charles Calima, Negros Occidental police director, said they are still investigating the motive behind Adevas killing.
Nenette, however, told investigators that her husband recently figured in a brawl in a dance hall and the three men might have retaliated because of the incident.
Adeva, who left five children, was affiliated with the militant Task Force Mapalad, although Calima said records showed that he was not involved in any controversial agrarian reform cases.