(UPDATE) MANILA - A self-confessed assassin on Thursday claimed Davao City Vice Mayor Paolo Duterte is a drug user and even masterminded several vigilante killings, accusations that the presidential son has denied.

Edgar Matobato, an alleged hitman of the Davao Death Squad (DDS), told a Senate committee inquiry that Duterte ordered the assassination of billionaire Richard King in 2014, due to an argument over a woman.

"Noong 2014, pinatay ang pinaka-bilyonaryo sa Cebu. Pinatay si Richard King sa Davao City. Ang nag-utos diyan, si Paolo Duterte," Matobato said at a Senate hearing on extra-judicial killings.

[In 2014, we killed a billionaire in Cebu. Richard King was killed in Davao City. The order came from Paolo Duterte]

But the vice mayor said there is no truth to any of Matobato's accusations, and called the witness as a "madman."

"What De Lima and this certain Matobato say in public are bare allegations in the absence of proof. They are mere hearsay," Duterte said.

"I will not dignify with an answer the accusations of a madman," he added.

Matobato claimed Duterte also unleashed the hit squad on another man who had an argument with him in 2010.

Matobato said two people, including an old woman who shielded the victim, were also killed in the DDS attack.

Matobato said the younger Duterte is also friends with Chinese drug lords. He also accused the younger Duterte of abusing illicit drugs.

"Ito si Paolo Duterte, maliit pa lang, ako na ang nag-e-escort, kami ni SPO2 Balaran... Matagal na 'yun, bata pa lang gumagamit na ng drugs," he said. [I have been a security escort of Paolo Duterte since he was young... He has long been using drugs, ever since he was young.]

"Minsan nagwawala iyan basta sabog iyan," the witness added. [He would sometimes run amok when he's high on drugs.]

The witness however admitted, after being questioned by Senator Alan Peter Cayetano, that he did not personally see the presidential son taking drugs.

Matobato earlier accused the vice mayor's father, President Rodrigo Duterte, of forming the DDS to kill suspected criminals.

READ: Self-confessed death squad member tags Duterte in killings

-- With reports from Vina Araneta, ABS-CBN News