Police are confident their case against Praween Chanklai, aka "Kamnan Nok", in the killing of a police officer, could lead to his death sentence, said Central Investigation Bureau (CIB) chief Pol Lt Gen Jirabhop Bhuridej.

The evidence can prove the suspect ordered the killing of Pol Maj Sivakorn Saibua, he said.

There were 15 security cameras installed at Mr Praween's house and after the shooting, in which Pol Maj Sivakorn was killed and Pol Lt Col Wasin Pandee, another highway police officer, was injured, two CCTV servers were removed and dumped into a canal.

Once the servers were retrieved, police salvaged files from 13 security cameras.

"The evidence we have points to Mr Praween as the mastermind. Witness statements, circumstantial evidence like the gun, the destruction of evidence and the motive are key components we have to get him the death sentence," he said.

Pol Lt Gen Jirabhop said police will gather as much as evidence as they can to make a strong case because the suspect and his accomplices have no respect for the law.

The CIB commissioner ordered police to gather information about influential figures in Nakhon Pathom for a planned crackdown to root out mafia-like gangs.

On Friday night, Pol Gen Surachate Hakparn, deputy national police chief, released CCTV images prior to the shooting and after the shooting.

"Most police at the party were armed but didn't try to intervene. Some aided the culprits and some senior officers fled the scene," said Pol Gen Surachate.