Three of 13 alleged gang members killed in a shoot-out with Philippine police were policemen, authorities said, as they began a probe into whether the violence was linked to illegal gambling.
The official police report following Sunday's incident in Atimonan town, 170 kilometres (100 miles) south of Manila, said security forces tried to block armed members of a criminal gang at a road block, setting off a battle.
However national police chief spokesman Generoso Cerbo said that among those shot dead was Senior Superintendent Alfredo Consemino, while two others killed were his aides.
Consemino was allegedly a partner of Victorino "Siman" Atienza, who operated a highly lucrative illegal numbers game called "jueteng", press reports said.
Cerbo said Atienza was killed in the gunbattle.
Cerbo would not confirm Consemino was a corrupt officer on the take, but said the allegations were being investigated.
"The investigation will try to find out why these police personnel were in the company of an alleged gambling operator," Cerbo said.
Cerbo said a police fact-finding team would also investigate claims by relatives of the dead that they were summarily killed and not slain in a gunfight.
"The official police report of our personnel on the ground said it was a shoot-out between the elements of a private armed group and the police and the military," Cerbo said.
"But with this allegation of a 'rub out' (slang for summary execution) we have decided to create a fact finding team to get to the bottom of this incident."
Press reports said Consemino may have been feuding with the police officer who led the team that manned the roadblock and who himself may be protecting another jueteng operator.
"We will (also) look into that particular observation," Cerbo said.
Jueteng is an illegal lottery known to generate hundreds of millions of pesos in proceeds, some of which finance campaigns by local politicians, officials have said.
Former president Joseph Estrada was ousted in 2001 by a popular revolt over allegations he received millions in kickbacks from jueteng operators in exchange for protecting them.
Corruption has long been a problem in the Philippines, including in the police and armed forces.
President Benigno Aquino, who came to office in 2010, has said fighting graft through all sectors of society is his administration's top priority.