Arturo Lascanas, a retired police officer, told the Philippine Senate that DDS members received money from the then-mayor in exchange for brutal killings of not only criminals but also of Duterte's enemies in politics and the media. At the time, Duterte was mayor of the southern Philippines city of Davao.
"We were motivated by the reward system ... when a killing is ordered and there's a price," he said. On top of payment for individual hits, he said that he had for 20 years received a monthly stipend of P100,000 (around $2,000) from Duterte.
The Philippines government has vehemently denied Lascanas' testimony, calling it a "fabrication."
"Lascanas tale on (Duterte's) alleged involvement in the EJK (extrajudicial killings) in Davao is a fabrication ... there is a contradiction between his statement in the press conference
and in his affidavit executed the day before he made the press conference," Sal Panelo, Duterte's chief legal counsel told CNN by text message. Lascanas also had appeared in front of the media last month.
"(Duterte) is outraged by any extrajudicial killing. Neither will he tolerate it. He abhors any violation of the Constitution or any law. Anything he does as President is pursuant to the constitutional duty of serving and protecting the people imposed on him by the basic charter."
The hearing is the first one under the Committee on Dangerous Drugs and Public Order.
Senator Leila de Lima, one of the President's harshest critics, said that she had "no doubt" that both Lascanas and Edgar Matobato,
another alleged DDS member who had come forward, were "credible."
"No doubt Lascanas' testimony, like that of Matobato is credible. Both Lascanas and Matobato are actual and direct participants in many incidents of killing as ordered by then Mayor Duterte. Their testimonies are based on their personal first hand knowledge, hence, admissible and worthy of credence," she said in a statement.
"From these revelations, the hard, ugly and inconvenient truth is that President Duterte has a criminal mind as he is in fact a criminal, a mass murderer at that."
De Lima was arrested on drugs charges last month.
She and her supporters maintain that the arrest is a politically motivated vendetta. She remains in detention and cannot participate in the hearings.
In a complete reversal of earlier statements, Lascanas testified before the Senate inquiry that he was part of the infamous group, which had operated in Davao from the mid-1990s to as recently as 2013.
In a Senate hearing in October 2016, he had denied being a member of the group
, refuting the sworn evidence of Matobato, who claimed in testimony in September 2016 to the Senate that he was a member of the DDS.
"There is no Davao Death Squad, your honor. That is all media hype," Lascanas said at the time.
The vigilante group was allegedly composed of men from specialized anti-crime police units as well as former militants, he said.
Lascanas said in Monday's testimony that he was personally responsible for the deaths of almost 200 individuals, including 30 innocent bystanders.
Lascanas said his motive for changing his story was his "desire to tell the truth, not only because of my spiritual renewal" but also because of his fear of God.
"I wanted to clear my conscience," he said. He added that he had lied in his previous testimony out of fear for his family's safety.
Testimony 'politically motivated'
Supporters of the President say that Lascanas' testimony is politically motivated.
One senatorial ally of the President, Sen. JV Ejercito, said he cannot allow "the Senate (to) be used for any destabilization plot" but only for the sake of ferreting out the truth.
"(You might be being used) to pin down the president, this administration," Sen. Manny Pacquiao, the boxer and another senatorial ally of the President, told Lascanas.
Another pro-Duterte lawmaker, Alan Peter Cayateno, suggested the drug gangs who were suffering at the hands of Duterte's national police force were behind pushes to oust the President.
At the hearing, representatives from the Philippines Commission on Human Rights (CHR) said they will open or resume investigations on the Davao Death Squad.
"Because this is a continuing investigation, the CHR will be conducting and calling on (Lascanas and Matobato) and requesting to submit their affidavits," Commissioner Roberto Eugenio Cadiz said.
Philippine National Police Director for Investigative group Gen. Marquez said the police will open investigations of unsolved cases based on Lascanas' testimony.
"We will dig up these records and we will match and find corroborating evidence," he said.