MANILA – Senator Panfilo Lacson on Monday said the momentum on the police's war on illegal drugs must not be deterred by any legislative inquiry, as the Senate started its probe on the extrajudicial killings in relation to President Rodrigo Duterte's bloody campaign against the drug menace.

Lacson, a former police chief, admitted he has misgivings about the Senate probe led by Senator Leila de Lima since the police's war on drugs have started to gain momentum.

''The momentum that the police [have] gained over a short period through life-risking work of fighting illegal drugs must not be deterred by legislative inquiries like what we are conducting right now. Frankly, I have never seen anything on this scale of the current anti-illegal drug campaign under this administration,'' Lacson said.

READ: Extra-legal killings hit as Senate launches probe on drug slays

Lacson said he sympathizes with the policemen, some of whom seemed to have lost faith in the country's justice system.

''I know their frustrations over a flawed judicial system with unsympathetic, sometimes corrupt prosecutors,'' he said.

''I know as well their enthusiasm to perform their duties in order to accomplish their assigned mission. I have openly and consistently manifested my misgivings to allow this inquiry to proceed and for good reasons," said Lacson.

The senator also acknowledged the dangers policemen face whenever they conduct operations.

''As I have spent almost half of my life in law enforcement, I am not sure how may times I could have been maimed or killed by enemy fire during police operations that I had participated in or the number of times I could have landed in jail while performing my duties,'' he said.

De Lima, in her opening statement for the hearing, said the unabated killings in relation to Duterte's war on drugs has been disturbing.

She said the inquiry aims to look into how alleged death squads could be masking their murders as part of the government's campaign against narcotics.

"I strongly believe that extra-legal killings, whether perpetrated by the state or by non-state actors, must stop. Blatant disregard for human life must stop,'' de Lima said.