Prime Minister Srettha Thavisin wants police to serve the general public instead of influential people, deputy national police chief Surachate Hakparn quoted the former as saying in their meeting on Sunday.
Pol Gen Surachate met the prime minister at Phitsanulok Mansion, the official residence of the prime minister.
There they discussed the case in which a highway police inspector was shot dead by a gunman who was close to a local administrator during a party at the administrator's house in Nakhon Pathom province on Wednesday night.
After the meeting Pol Gen Surachate said the prime minister told him to suppress influential people.
"The prime minister emphasised the suppression of mafias and influential people in localities so that [ordinary] people have confidence in their own safety. Police must not support those influential figures... The prime minister said police must be on the people's side," Pol Gen Surachate said.
The deputy national police chief said the police officers who were at the dinner party in Nakhon Pathom lied during initial interrogation after the fatal shooting on Wednesday.
"OK you can lie but we have interrogation, investigation and clear information," Pol Gen Surachate said.
He confirmed that culprits would face legal action as long as evidence would prove their wrongdoing.
The evidence included a CCTV server at the local administrator's house. It was reported that a corrections official threw it into water in a bid to conceal crime, Pol Gen Surachate said. He referred to CCTV footage at the house of Praween Chankhlai, a 35-year-old kamnan (subdistrict chief) in Nakhon Pathom.
The server was already dry, and its data would be completely recovered in three to four days, Pol Gen Surachate said.
"Some police officers will definitely be held responsible in the case," he said.
According to him, the police officers who joined the dinner party at Mr Praween's house fell into three groups.
One was the group of the officers who fled the house just after the shooting. The second group contained the officers who destroyed evidence and brought Mr Praween away from the crime scene. The other group rushed the shot inspector to hospital.
Regarding the questioning of witnesses and suspects, Pol Gen Surachate said that all of them fingered Mr Praween as the one who ordered the shooting.
"There was a request for a police transfer. When it was rejected, he ordered the shooting... He was so close to local police for so long that he was excessively confident. Today this must be eliminated," Pol Gen Surachate said.
Mr Praween continued to deny all charges but he could not escape, the deputy national police chief said.
Praween Chankhlai, the kamnan who allegedly ordered the shooting. (Photo supplied)