The Naha District Court found Kenneth Franklin Shinzato, 33, guilty of killing 20-year-old Rina Shimabukuro in April last year. The court ruled that the April 2016 crime was committed with "selfish motivation, which left no room for leniency", reported Japanese news agency Kyodo.
The defendant, a member of the US Navy between 2007 and 2014, who was working as a civilian at the Kadena base in Okinawa at the time of the incident, had admitted to the charges of rape resulting in death and abandoning the body of the victim, but denied intent to murder, the BBC reported.
According to the indictment, Shinzato stabbed the girl in the neck and hit her on the head with a rod so that she would not resist, killing her as a result. However, the defendant said at the trial that he "did not intend to cause such a result".
The case once again triggered public outrage and intensified public resentment against excessive US military deployment and the crimes committed by US servicemen in the region.
The most serious of these cases occurred in 1995 when three soldiers from an Okinawa base kidnapped and raped a 12-year-old girl, prompting some 85,000 people to protest.
In 2013, two US sailors admitted to raping a woman.
In the most recent case, a 60-year-old Japanese man died after a military truck driven by an allegedly drunk marine collided with his vehicle on November 19.
The US and Japanese governments have been trying to relocate part of a large airbase to a less populated area of the island, but many Okinawans want it removed altogether.
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