Metro Manila (CNN Philippines, May 9) — President Rodrigo Duterte's son, former Davao City Vice Mayor Paolo Duterte, is under investigation for graft and four other cases, sources at the Ombudsman confirmed on Wednesday.

A list of the cases show the younger Duterte is also charged with perjury, forfeiture, violation of the code of conduct and ethical standards, and conduct prejudicial to the best interest of government service, grave misconduct, and serious dishonesty.

Of the five cases, two are criminal, two are administrative, and the one on foreiture involves ill-gotten wealth.

The sources did not specify the actual cases or their details, but said investigators found sufficient basis to elevate them to the preliminary investigation stage.

Paolo Duterte, in a Facebook post, said this was an old, "recycled" story.

A case on the alleged involvement of the former vice mayor in the smuggling of P6.4 billion shabu to the country was excluded as this was already dismissed on May 2.

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Ombudsman Conchita Carpio Morales on Tuesday confirmed there were other pending cases against Paolo Duterte in her office, but declined to provide details.

Morales, who is due to retire in July, said she had already inhibited herself from all cases against the Duterte family. A nephew of the Ombudsman is a son-in-law of President Duterte.

Presidential Spokesperson Harry Roque said the Ombudsman is exercising its power to investigate and initiate proper action against public officers.

"We see this as part of the Ombudsman's constitutional mandate to ensure public accountability," he said in a statement.

CNN Philippines' AC Nicholls contributed to this report.