TOKYO — A U.S. sailor was sentenced Thursday to life in prison in the stabbing death of a Japanese taxi driver, a crime that led to calls for tougher punishment for American service members who break the law.

Olatunbosun Ugbogu, a 23-year-old Nigerian citizen serving in the U.S. Navy, was found guilty of stabbing 61-year-old Masaaki Takahashi to death near a U.S. naval base in Yokosuka in March 2008, according to a Foreign Ministry official.

Ugbogu was initially apprehended by U.S. Navy authorities in Tokyo on a desertion charge, but was handed over to Japanese authorities because a credit card in his name was found in the victim's car.

Presiding Judge Masaaki Kawaguchi ruled that Ugbogu, who testified that he heard "voices" ordering him to kill Takahashi, was mentally competent to stand trial, according to Kyodo News Agency.

The U.S. Navy in Japan said after the ruling that it has "full faith in the Japanese judicial system and is confident justice was served."

"The U.S. Navy continues its policies of enforcing discipline and teaching our sailors and their families to be better members of the local communities," it said in a statement.