Senator Ronald "Bato" dela Rosa, the former police chief and top enforcer of ex-President Rodrigo Duterte's bloody "war on drugs", is wanted for crimes against humanity, the same offences Duterte is accused of, and had been under the Senate's protection since Monday.
Gunshots were heard late on Wednesday inside the heavily-guarded Senate, hours after dela Rosa, 64, appealed on social media for supporters to mobilise, saying agents were coming to arrest him.
His ally, Senate president Alan Peter Cayetano, said on Thursday he was no longer there and read to reporters a text message that he said was from dela Rosa's wife, apologising for the turmoil that his presence had created.
"It's for this reason I'm sure Ronald made his escape," said the text message from Nancy dela Rosa.
The message did not disclose dela Rosa's whereabouts but said fleeing "was not part of the plan".
The Senate stand-off is a major challenge to the authority of President Ferdinand Marcos Jr, whose government was unable to confirm on Thursday if dela Rosa had fled.
Marcos is embroiled in a bitter and long-running battle with the influential Duterte family and has insisted he gave no order to arrest dela Rosa, a staunch loyalist of the former president.
Dela Rosa's appeal for help on social media led to chaos on Wednesday, with a hefty presence of police and armed guards at the Senate, protests outside and more than a dozen shots fired just moments after a marine detachment was called in to bolster security.
Police said investigations were under way, with bullet casings and assault rifle magazines recovered and one person detained who had "provided names" that were being verified.
The ICC unsealed a warrant on Monday for dela Rosa's arrest.
He has filed an emergency appeal at the Supreme Court, arguing the ICC has no jurisdiction after the Philippines' 2019 withdrawal from the Rome Statute.
The tough-talking dela Rosa enjoyed celebrity status as Duterte's top lieutenant, overseeing a fierce crackdown during which thousands of alleged drug dealers were slain, with rights groups accusing police of systematic murders and cover-ups.
Police reject that and say the more than 6000 killed in Project Double Barrel were all armed and had resisted arrest.
In a radio interview with DZBB, dela Rosa said he would "exhaust all available remedies" to block his ICC transfer and having learned about conditions Duterte was enduring, he was no longer willing to fight his case in The Hague.
Both dela Rosa and Duterte have denied inciting police to commit murders.
Political tension has been boiling over since Monday, with drama following dela Rosa's emergence from six months of hiding and the impeachment of the ex-president's daughter, Vice-President Sara Duterte, Marcos' former running mate.
Marcos relied on support of the Duterte family to win a 2022 election before a falling out that led to him handing Rodrigo Duterte over to the court in The Hague.
