The Special Branch Bureau is probing a police sergeant, who has been accused of attempting to rob a Kasikornbank branch in Chachoengsao despite his claim that he was on a mission.
The officer, whose name has been withheld, was seen walking suspiciously in front of the bank in the Bang Wua area of Bang Pakong district yesterday before he was detained for questioning.
Investigators were initially told that he was attached to the Special Branch Bureau and was part of a team assigned to observe the behaviour of suspects.
"He claimed he was on duty to arrest a wanted suspect," deputy police spokesman Kissana Phathanacharoen said.
The officer was in plainclothes, had his face covered, and was also carrying a pistol.
It remains unclear whether the man was actually part of a crime crackdown.
If there is no evidence to support his claim, the man will face a weapons charge, Pol Col Kissana said.
The investigators are treating the probe seriously after national police chief Chaktip Chaijinda ordered all police units to keep a watch on their officers and act against them if they behave in an unacceptable manner.
It has been found that many officers are facing transfers or other disciplinary action as they have been suspected of misconduct or ignoring their duty.
Earlier this month, Nonthaburi police chief Pol Maj Gen Paisarn Wongwatcharamongkhol was transferred to an inactive post after an April 8 raid on a gambling den in Muang district within his area of supervision.