President Ferdinand Marcos Jr. on Friday made derogatory remarks about former Philippine Drug Enforcement Agency (PDEA) agent Jonathan Morales, calling him a "professional liar."

The Chief Executive made the comment in a media interview in General Santos City amid the Senate's ongoing investigation into PDEA's purportedly leaked documents dated 11 March 2012, which allegedly linked Marcos and actress Maricel Soriano to illegal drug use.

Morales, during the Senate committee hearing earlier this week, claimed that Marcos was included in the pre-operation report and authority to operate the anti-drug agency.

Last 2 April, PDEA already cleared Marcos from the purported inclusion in a drugs watchlist saying that the documents were not located in PORMIS, or Plans and Operations Reports Management Information System.

PDEA Director General Moro Virgilio Lazo has also reaffirmed that Marcos was never on the agency's narcotics watchlist.

"You know, (Morales) is a professional liar, like a jukebox. Whatever you drop in --- as long as you drop money, whatever song you want, he'll sing it," Marcos said in Filipino.

"Things don't make sense. Just look at his --- he has a case of false testimony. That's how it is. How many... He has a history of involvement with various people and situations. It seems like that's his livelihood, that's why I call him a professional liar," he added.

Senator Jinggoy Estrada revealed that Morales had been charged with many crimes in local courts, including infractions of Article 180 of the Revised Penal Code (RPC) pertaining to false evidence.

"The facts and evidence presented clearly demonstrate the questionable integrity and credibility of this particular resource person, and the same evidence refutes all accusations against the PDEA and its current leadership. The statements given by this particular resource person against the agency and leadership are evidently perjurious, defamatory, and outright false," Estrada said.

During the celebration of the GOCC day at the PICC in Pasay City earlier this month, Marcos has already shrugged off the issue of the PDEA documents dragging him and Soriano in illegal drug use.

Marcos simply laughed and walked away when asked by reporters about the issue, while Executive Secretary Lucas Bersamin described the claim as "contrived."