(UPDATE) THE Senate said Monday it will conduct a probe of ex-president Rodrigo Duterte's arrest and swift handover last week to the International Criminal Court (ICC), which is to try him for alleged crimes against humanity.

The 79-year-old, the first Asian former head of state charged by the ICC, stands accused of the crime against humanity of murder over his years-long campaign against drug users and dealers that rights groups have said killed thousands.

The probe was initiated by Sen. Imee Marcos, sister of President Ferdinand Marcos Jr. but a close friend of Duterte's eldest daughter, Vice President Sara Duterte.

The two families have had a spectacular falling out since Marcos teamed with Duterte to win an election landslide in 2022. The latter has since been impeached on charges that include an alleged assassination plot against the president.

"As chairperson of the Senate Committee on Foreign Relations, I am calling for an urgent investigation into the arrest of former president Rodrigo Roa Duterte, an issue that has deeply divided the nation," Imee Marcos said in a statement Monday.

"It is imperative to establish whether due process was followed and to ensure that his legal rights were not just upheld but protected," she said, adding: "Our sovereignty and legal processes must remain paramount."

Duterte was arrested at the Ninoy Aquino International Airport on March 11 after a brief trip to Hong Kong and flown to the Netherlands just hours later where he was turned over to the ICC.

The Senate has set a public hearing for Thursday and invited top police and other government officials to give evidence.

Imee Marcos has tracked a course largely independent from her brother on many issues, though she is running for re-election under the administration ticket for the May 12 midterm elections.

Hours after the arrest, she challenged the wisdom of the arrest of "poor president Duterte," warning at a news conference: "This can only lead to trouble."

On Friday, she declared: "I cannot accept what they did to [Duterte]."

Marcos earlier said that Duterte's arrest would only cause chaos and said she pitied the former leader. Duterte is set to turn 80 on March 28.

Malacañang said it would not bar any government official from participating in the Senate inquiry.

Presidential Communications Office (PCO) Undersecretary and Palace Press Officer Claire Castro issued the statement in response to the lawmaker's push for a congressional probe on the legality of Duterte's arrest and his eventual turnover to the ICC.

"If that is the desire of the senator, she is free to do that," Castro said in English and Filipino in a press conference.

The senator said she is mulling summoning officials from the Philippine National Police, Department of Justice, National Security Council, Civil Aviation Authority of the Philippines, and the Office for Transportation Security-Department of Transportation, to the Senate investigation.

Castro said she does not see any reason for the Palace to order them to not attend the hearing.

"If the inquiry is in aid of legislation we will respect the request of Senator Imee," she said while also expressing confidence that whoever would be facing the inquiry can effectively answer and justify all issues which may be raised given that the aforementioned agencies "complied with all the requirements with the law regarding the arrest of former president Duterte."

Castro reiterated that there was nothing irregular with the pronouncement of Interior and Local Government Secretary Jonvic Remulla that he, National Security Adviser Edgardo Año, Defense chief Gilbert Teodoro, and the president convened to discuss Duterte's arrest.

The former leader was arrested last March 11 by virtue of an arrest warrant issued by the ICC and enforced by the International Criminal Police Organization, or Interpol.

"There shouldn't be any criticism if they had a meeting because it was about helping the Interpol. There is nothing wrong with that," Castro said.

'Kidnapping'

Meanwhile, former presidential spokesman Harry Roque described Duterte's arrest and extradition to the ICC in the Hague in the Netherlands as an act of "kidnapping," asserting that the procedure violated the Rome Statute's due process requirements.

Roque, who is currently in the Hague assisting in the defense of Duterte, also expressed serious concerns regarding the potential legal liability of President Marcos, Año, Teodoro, and Remulla over the what he described as a government-orchestrated abduction and subsequent transfer of the former president to the ICC.

"It was a kidnapping. According to Article 59 of the Rome Statute, if an accused is to be surrendered to the ICC, he must first be presented to a 'competent judicial authority' — a local Filipino judge and court — to validate the warrant, confirm the identity of the accused, and ensure that his rights were upheld during the arrest," Roque said.

However, political science professor Antonio Contreras said Article 59 does not apply to Duterte's case.

"The truth is simple: Article 59 applies only when the custodial state — the country where the suspect is arrested — is a state party to the Rome Statute. It does not apply when the suspect is in a nonmember state," Contreras wrote in his column in The Manila Times.

"Rodrigo Duterte, the former president of the Philippines, is a national of a nonmember state, and he was arrested within the territory of the Philippines, a state that withdrew from the Rome Statute in 2019, thanks to Duterte himself," he added. "This means that the Philippines, as a nonmember state, is under no treaty obligation to adhere to Article 59 or any other provisions of the Rome Statute."