The warrant, expected to be approved in the afternoon, was backed up by solid evidence and witnesses, said Samut Sakhon police chief Pol Lt Gen Harnpon Nitwiboon on Monday.
Udorn Kraiwatnusorn, 49, had stopped for petrol at a PTT filling station and was walking to the restroom when an unknown number of men followed him from the parking lot and fired at him. He was hit by six bullets and died at the scene.
Udorn, the eldest son of former deputy agriculture minister Monthon, would have completed his second term as PAO president in April.
Harnpon told reporters that initial investigation showed that Udorn, a member of Pheu Thai Party, had personal conflicts with the killer who he said is a member of the Democrat party.
“We have information that whenever Khun Udorn and the suspected killer met, they argued fiercely. This may have lead to the killing,” he said.