A United States Marine convicted of killing a transgender woman in the Philippines in 2014 has been granted an "absolute pardon" by President Rodrigo Duterte in a case that sparked outrage over alleged preferential treatment given to American military personnel on assignment in the country.

Lance Cpl. Joseph Scott Pemberton has served about six years of the 10-year sentence he was given in 2015 for killing Jennifer Laude, a 26-year-old transgender woman, in a motel room in 2014.

Duterte's action was announced by Philippine Foreign Affairs Secretary Teddy Locsin Jr. on Monday and confirmed by Presidential Spokesperson Harry Roque in a report by the state-run Philippine News Agency (PNA).

It came after a court last week said Pemberton should be given credit for good conduct during his time served in the Camp Aguinaldo military prison in Quezon City, rather than New Bilibid Prison, the country's main penitentiary, according to a CNN Philippines report.

That credit amounted to more than four years, the court said, and with time served after his arrest but before trial, Pemberton had served the 10 years required.

Critics said it was easy for Pemberton to be on good behavior because he was able to serve his sentence alone rather than with the general prison population.

"Cutting matters short over what constitutes time served, and since where he was detained was not in the prisoner's control and to do justice the President has granted an absolute pardon to Pemberton," Locsin said in a Twitter post.

Pemberton's lawyer, Rowena Flores, said Duterte's decision was not something her client sought and that she first learned of it from the media.

"I thank our President for his pardon. I think with this development, justice is served and that the laws were followed," she told CNN Philippines.

Duterte, speaking in his weekly address on Monday, said no records were kept on Pemberton's behavior in the military prison so he should be assumed to have acted properly.

"You have not treated Pemberton fairly, " Duterte said, according to PNA.

"We should allow him the good character presumption."Pemberton was 19 at the time of his conviction.

He was convicted of the lesser charge of homicide, rather than murder, after the court determined that Pemberton had not acted with "treachery."

Supporters of the late Jennifer Laude hold up her image during a protest near a Philippine court in Olongapo, north of Manila on February 23, 2015.

The naked body of Laude was found with her head in a toilet in an Olongapo hotel room shortly after midnight on October 12, 2014, police said after his arrest.

Witnesses told police that Pemberton was with Laude at a local disco before the two checked into a hotel on the night of October 11, according to documents seen by CNN.

Pemberton told police that he'd choked Laude, but then tried to revive her.

He said he had become angry with Laude upon discovering she had male genitalia, according to police.

Pemberton, from Massachusetts, was an anti-tank missile man assigned to 2nd Battalion, 9th Marines, out of Camp Lejeune, North Carolina.

He was in the Philippines for military exercises being conducted under the Visiting Forces Agreement (VFA).

Signed in 1988, it gives US military aircraft and vessels free entry into the Philippines and relaxes visa restrictions for US military personnel.

But it gives the Philippines primary jurisdiction over US military personnel accused of crimes in the country, unless those crimes involve other US troops.

The Philippines was once home to two of America's largest military bases outside of the US: Clark Air Base and Subic Bay Naval Station.

Although those ceased to be US bases in the early 1990s, US forces still had access to them under the VFA.

The hotel where Laude was killed was outside Subic Bay. Pemberton was on leave after participating in the military exercises.

Sen. Imee Marcos said the pardon served justice under Philippine law while helping relations between Manila and Washington.

"Justice has been served with the Philippine judicial system functioning in accordance with its constitutional duties," she said, according to CNN Philippines, while preserving "very deep and very cordial" relations with the US.

CNN has reached out to the US Embassy in Manila for comment.

Relations had been strained in February when Duterte gave the US 180 days' notice to end the VFA, suggesting that Manila needed to rely on its own resources for its defense.

He reversed that decision in June "in light of the political and other developments in the region," Locsin said in a social media post at the time.

The reversal came as China was stepping up its military presence on islands in the South China Sea that are claimed by the Philippines.

On July 12, the Philippines for the first time formally recognized a 2016 ruling by the United Nations Permanent Court of Arbitration siding with Manila and against Beijing over China's claims on contested islands in the South China Sea.

Two days later, Washington announced a formal rejection of "most" of China's maritime claims in the South China Sea.

Critics of Pemberton's pardon on Monday blamed the Philippine government for putting military relations above the rights of Philippine citizens.

Edre Olalia, president of the National Union of Peoples' Lawyers, called the pardon "unbelievable".

"What makes it even more atrocious is that his entitlements and liberty were apparently politically bartered through an onerous and servile military agreement.

"What cheap price sovereignty and national dignity," he said in a statement, according to CNN Philippines.

Pemberton's lawyer said he would still need to comply with certain legal requirements before he could leave the country, but she was hopeful that would happen before the end of the week, CNN Philippines reported.

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