Commandos in pursuit of the notorious Malaysian bomb maker Zulkifli bin Hir, also known as Marwan, took a DNA sample from the scene of their assault on their target, and passed it to the FBI for testing.
Marwan -- believed by the FBI to a member of southeast Asian terror group Jemaah Islamiyah's central command -- had previously been falsely reported dead after a raid by Philippine security forces in 2012.
But preliminary results from the tests showed a link with a known relative of Marwan, said David Bowdich, assistant director in charge of the FBI's Los Angeles field office.
While the testing could not yet provide "absolute identification," he said, "the results do support that the biological sample provided by Philippine authorities came from Marwan."
Marwan's brother, Rahmat bin Hir, is in a California prison following a 2007 arrest for conspiracy to provide "material support to terrorists."
The FBI has been offering a $5 million reward
for information leading to Marwan's capture, in the wake of his 2007 indictment on terror charges in a California court.
It accuses him of being a supplier of IEDs to terrorist organizations, and having conducted bomb-making training for terror groups, including the Philippines-based Abu Sayyaf.
"He was the leader of Jemaah Islamiyah within the Philippines, the most senior figure," said Clarke Jones, a terrorism expert at Australian National University, who works on de-radicalizing Islamist terrorists in Philippine prisons.
The Philippines has been fighting an insurgency in the predominantly Muslim south for years, and last year signed a peace agreement with the Moro Islamic Liberation Front (MILF), the largest rebel group in the region.
Marwan, was believed to be affiliated with the Bangsamoro Islamic Freedom Fighters (BIFF), a hardline splinter group which rejected the peace deal, and had claimed responsibility for bombings in the region, said Jones.
At large since 2003, he had been able to operate in relative safety from his base in the southern Philippines, said Jones.
He said the killing of Marwan would "without a doubt" disrupt the BIFF's activities.
"He was a key agitator in disrupting the peace accord between MILF and the Philippines government," he said.
"This is a major blow to the militants down south."
The mission to get Marwan late last month
went disastrously awry, with 44 members of the police's elite Special Action Force (SAF) unit killed in a 12-hour firefight after ambushing the bomb maker in the southern province of Maguindanao.
Authorities said that as commandos were retreating from their assault, they came under fire from members of the BIFF.
In maneuvering away from the BIFF onslaught, they strayed into territory controlled by the MILF, and further fighting ensued, shattering a three-year ceasefire.
A national day of mourning
was declared as the men were laid to rest.
In a eulogy, the deputy director of the Special Action Force, Police Chief Superintendent Noli G. Talino, expressed his guilt at having failed to safely extract the fallen men.
"Is it worth it? One international terrorist equivalent to 44 SAF troopers?" he asked. "I'm sure if you will ask them, it is worth it."