A teenager who was arrested over an alleged online threat may have been prompted by police to admit guilt, as the boy's written statements described the method employed and his supposed motive in an unnatural way, according to investigative sources.

The 19-year-old boy was arrested by the Kanagawa prefectural police and later put on probation on suspicion of posting a threat to attack a primary school on the Yokohama municipal government's website.

It also has been found that the Yokohama District Public Prosecutors Office compiled a report of his confession with content largely matching that of the boy's written statements.

Investigative authorities are looking into the case based on the possibility the police used leading questions to induce the boy to admit to the allegations, the sources said.

On Saturday, the prefectural police admitted they wrongly arrested the boy and offered him an apology. The prosectors office also apologized the same day.

According to the sources, the boy initially denied the allegation that he posted a threat on the Yokohama municipal government website during the questioning conducted on a voluntary basis.

But a couple of days after his arrest on July 1, he reportedly gave written statements confessing to the allegations. The next day, however, he again denied the charges. Then, during interrogations by the Yokohama District Public Prosecutors Office, boy again admitted to the allegation. The prosecutors office compiled the report of his confession.