MANILA -- Former Philippine president Rodrigo Duterte was arrested on Tuesday, just weeks before his 80th birthday, on the charge of committing crimes against humanity during the deadly years-long drug war that was his signature policy.

Other former Philippine leaders have been arrested before, including Joseph Estrada in 2001 and Gloria Arroyo in 2011, both on graft charges, but Duterte is the first potentially to face an international tribunal.

AFP below looks at the case before the International Criminal Court (ICC) and how it unfolded:

Why was Duterte arrested?

The Senate Blue Ribbon Committee secretary administers the oath of former President Rodrigo Roa Duterte Monday, October 28, 2024 before he begins his testimony before the subcommittee investigating motu proprio the alleged extra-judicial killings during his administration. Senate Public Relations and Information Bureau/FileThe Philippines' prosecutor general acted after Interpol Manila received a copy of the ICC warrant early on Tuesday, according to the presidential palace.

Duterte was taken into custody at Manila airport shortly after stepping off a plane following a visit to Hong Kong.

The arrest warrant specifically cites "murder as a crime against humanity" in connection with his violent drug war.

The tribunal has been investigating the Duterte government's drug war since September 15, 2021. Thousands were killed during the campaign, mostly poor men.

The ICC reinstated the investigation in 2023 after a break in proceedings following an appeal by the Philippines.

While estimates of those killed vary, prosecutors at the Hague say "the total number of civilians killed in connection with the so-called 'war on drugs' campaign" ranges from 12,000 to 30,000.

Duterte was in power from June 2016 to June 2022.

READ: Ex-President Duterte arrested on ICC warrant

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How has the Philippine government treated the case?

The Duterte government had a long-standing policy of refusing to cooperate with the ICC probe, saying it lacked jurisdiction and infringed on the country's sovereignty.

Duterte instructed his government to pull out of the ICC's founding treaty, the Rome Statute, after the tribunal began looking into allegations of systematic extrajudicial killings during his rule.

However, the tribunal ruled that alleged crimes committed before Manila's withdrawal from the treaty in 2019 remained under its jurisdiction.

Current President Ferdinand Marcos refused to resume ICC membership after he was elected in 2022, with Duterte's daughter Sara as his vice-presidential running mate. He also continued to rule out any cooperation with the ICC probe.

However, Marcos's stance shifted subtly as the alliance between the two powerful families unravelled. He said Manila would comply, under its obligations as an Interpol member, if the ICC sought Interpol's help in arresting Duterte.

READ: Sara Duterte back in Philippines after father's arrest

What happens next?

Kristina Conti, a Philippine lawyer serving as assistant to counsel in the ICC case, said it was possible Duterte would be flown out on the next available flight to a detention facility "nearest" to the ICC, which is based in The Hague in the Netherlands.

She said the arrest warrant specifically instructs the officers who served it to "bring the accused to the court, and the court is in The Hague".

What has Duterte said about the case?

When the drug war case was first filed in the ICC, Duterte insisted the tribunal lacked jurisdiction and that he would only be willing to be arrested and tried in a Filipino court.

Duterte told hundreds of cheering supporters at a rally in Hong Kong on Sunday that his actions during the drug war were meant "to provide a semblance of peace and quiet" for Filipinos and everything he did was "for my country".

He also said he would "accept it" if he were arrested.

However, Duterte quickly challenged his detention's legality in a clip posted to social media after his arrest on Tuesday.

"What is the law and what is the crime that I committed? Prove to me now the legal basis for my being here," he said.

© Agence France-Presse