"We are still investigating the incident, including the identity of the persons who lobbed the grenade and why they attacked the project site," Chief Inspector Benjamin Marcial, Tupi police chief, told The STAR.
Marcial said the probers were focusing their investigation on the alleged "leadership struggle" among the DARBCI officials and members.
After the grenade explosion which was heard across Barangay Kablon, the attackers lobbed a container filled with gasoline in the livestock area.
The projects caretaker, a certain Reynante Rufino, 19, survived the attack.
DARBCI officials urged the police to conduct a thorough investigation into the attack.