TOKYO - A former United States Marine based in Japan's south-western island of Okinawa was on Friday (Dec 1) sentenced to life in prison for the rape and murder of a local woman.

Kenneth Franklin Shinzato, 33, who had served as a Marine from 2007 to 2014, was a civilian worker at the US Air Force's Kadena Air Base at the time of the crime on April 28 last year. He confessed at the Naha District Court to the rape of 20-year-old Rina Shimabukuro on April 28 last year as well as the subsequent abandonment of her body, but fought the murder charge claiming that he did not have any intent to kill.

Ms Shimabukuro's body was only found on May 19 last year.

District Judge Toshihiro Shibata, in finding Shinzato guilty of murder, said on Friday: "The immeasurable viciousness of the accused led to the senseless killing of a young woman, who only just came of age."

Chief Cabinet Secretary Yoshihide Suga told a news conference on Friday: "This was an extremely cruel and evil incident that deprived the life of a young woman with a future ahead of her."

He added: "There should be no more incidents, nor accidents, by the US military."

The crime committed by Shinzato - whose own name is Gadson but chose to use his Japanese ex-wife's name - outraged Okinawa citizens who have long resented the presence of US military bases and their attendant noise on the strategically-important island.

A spate of crimes committed by the US servicemen against local citizens have worsened the tension.

Just last month, US Marine Nicholas James-McLean, 21, was arrested after his truck collided with a vehicle driven by 61-year-old Hidemasa Taira. James-McLean's blood alcohol content was three times the legal limit.

And in the most infamous case, in 1995, three US servicemen kidnapped and gang raped a 12-year-old girl, sparking mass anti-American demonstrations.

These crimes, as well as safety concerns after a series of aircraft emergency landings and crashes, has intensified local opposition to US military presence on Okinawa, which despite its small size hosts almost 75 per cent of the land allotted for US bases in Japan and where about 26,000 US personnel are stationed.

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In Shinzato's case, prosecutors called for a life sentence for what they described as a premeditated crime.

According to the indictment, Shinzato clubbed Ms Shimabukuro with a bar, before dragging her to a grass field where he strangled her and then stabbed her several times around the neck to stop her from resisting his advances.

Prosecutors noted that Shinzato had, in fact, left his home that day in a car with a large suitcase filled with dirt. After he killed his victim, he squeezed her corpse into the suitcase, which he covered with dirt and abandoned in a forest.

Shinzato testified last month that although he had intended to knock his victim unconscious and rape her, he did not harbour any intention to kill her. He claimed that he planned to let the woman go after raping her.

Shinzato's case was heard under the lay judge system, under which locals hear the case alongside professional judges.

He had requested his trial to be heard outside Okinawa, saying that anti-US sentiment meant he would unlikely have received a fair trial. But this was denied by the Supreme Court last year.

Lieutenant-General Lawarence Nicholson, commanding general of the US Marine Corps Forces in Japan, had said last month at a news conference called on the day of the hearing: "I speak for all Americans - I am still shocked and I find it hard to understand how anyone could commit such a crime."