Japan police arrest teen for 'Islamic State-inspired' killing

The brutalised and naked body of Ryota Uemura was found in undergrowth near a river last Friday. His neck and been repeatedly hacked at, apparently using a blood-soaked knife that was discovered nearby.

Low-crime Japan has been captivated by the killing, with media reporting every twist and turn in the investigation, including details of how the youngster's mobile phone was used to send a friend request on a messaging app around the time of his death.

Populist weekly Shukan Shincho reported the wounds appeared to indicate that whoever killed Ryota may have been trying to decapitate him.

"Some investigators suspect (the criminals) watched Internet videos showing the execution of hostages by Islamic State (IS) fighters and sought to mimic them," the magazine said, quoting an unnamed source close to police.

Japan is still reeling from the brutal murder of two of its citizens, war correspondent Kenji Goto and his friend Haruna Yukawa, by Islamist extremists in Syria.

Kanagawa Police Department on Friday arrested an 18-year-old boy, whose name was withheld because he is legally a minor, on suspicion of murder, public broadcaster NHK and other news reports.

While a police spokesman declined to confirm the reports, investigators also obtained arrest warrants for two other teenagers over the murder in Kawasaki, an industrial city southwest of Tokyo, media said.

Junior high school student Ryota reportedly knew the suspects, and had been attacked by them previously, media said.

Violent crime is exceedingly rare in Japan and becomes very big news when it occurs.