The Chiba District Court sentenced four teenage boys Thursday to prison for up to 10 years for murdering a 16-year-old girl last year.
The court sentenced three of the four to between five and 10 years in prison for beating to death Yuko Ishibashi, a bar waitress, and burning her body.
The other boy, who beat Ishibashi but did not help to burn her corpse, was handed a sentence of 3 1/2 to seven years.
Presiding Judge Kenji Katoya said: "It was a well-planned, cruel crime. Their destroying the body indicates they have no remorse toward the dead."
The names of the four, aged between 17 and 19, were withheld because they are minors.
They were found guilty of conspiring with Hironobu Suzuki, 22, who is being tried separately, to kill Ishibashi by hitting her in the head with stones and hammers in a parking lot in the city of Chiba during the early hours of Oct. 1.
Three of the boys and Suzuki then poured oil over the girl's body and set it on fire.
Suzuki had married Ishibashi on paper and adopted her family name so he would be able to get more loans from moneylenders. The court said he decided to kill Ishibashi because she threatened to tell police about his reason for marrying her.
Suzuki persuaded the four youths to help him murder Ishibashi by telling them that she had revealed that they mugged people, the court said.