Metro Manila (CNN Philippines, February 14) — Magdalo Party-list Rep. Gary Alejano said he found notable patterns in some of the casualties of the Duterte administration's controversial war on drugs.

Alejano, a staunch critic of President Rodrigo Duterte, said some of the dead in "Oplan Tokhang," the police's anti-illegal drug program, were killed using .38-caliber firearms and weapons with unspecified, defaced or altered serial numbers.

Alejano said this could give an impression that the same weapons were being planted as evidence in these operations over and over again.

"Importante ito na walang serial number, na defaced, dahil pwede mo ulit-ulitin yan na pang-tanim," he said. "Ang importante, kung ilan ang na-recover, 'yun din dapat ang nakikita natin na ini-store ng PNP dahil pwedeng ulit-ulitin talaga."

[Translation: The fact that there is no serial number or that the number is defaced is important because you can plant the gun again and again. What's important is that the firearms recovered in operations should be the same firearms in the PNP's inventory because these can really used repeatedly.]

The lawmaker said he based his inference on the 1,005 Tokhang spot reports that the Philippine National Police (PNP) submitted to the House of Representatives. The reports involve 1,671 casualties recorded from July 2016 until November 2017.

Alejano, however, admitted that the data they received may not yet be conclusive since the spot reports only account for one in four of the nearly 4,000 reported casualties.

Based on the spot reports, Alejano also discovered that most deadly "Tokhang" operations were conducted from 6 p.m. to 5:59 a.m.

Alejano believes that conducting the operations during these hours could help conceal police personnel for improved apprehension of drug suspects.

But he also believed that the PNP may be purposely conducting its operations during these inconspicuous hours to conceal their activities from witnesses.

Alejano added that most of the casualties were men aged 21 to 40 who were found to be carrying one to six sachets of shabu.

The return of 'Tokhang'

The PNP relaunched "Tokhang" in January 2018. It had first implemented the campaign from July 2016 to October 2017 when it was suspended.

Read: Police resume anti-illegal drug operations under new guidelines, emphasizes human rights

The program's suspension came amid alleged extrajudicial killings in these operations. President Rodrigo Duterte then ordered the Philippine Drug Enforcement Agency (PDEA) to take over the drug war.

Read: No more 'Oplan Tokhang': Police suspends all anti-drug operations

However, Duterte allowed the police to conduct anti-illegal drug operations in December 2017.

Read: Duterte allows police to go back to drug war

Official records show that less than 4,000 drug suspects were killed in legitimate police operations: 34 by PDEA agents and 3,933 by the police.

These allegedly included the killing of teenagers Kian Delos Santos, Carl Arnaiz, and Reynaldo de Guzman.

Related: What we know so far about Kian's death

CNN Philippines Digital Producer VJ Bacungan contributed to this report.