Tokyo, Feb 4 (IANS/EFE): A Tokyo court Wednesday sentenced a 32-year-old man to eight years in prison for sending, remotely through third party computers, messages threatening mass murders at schools, fairs and the bombing of an airliner.

The court found Yusuke Katayama, a former employee of a telecommunications company, guilty of introducing a virus which he created himself into the computers of four people and remotely controlling their systems to send threats to the police and the media.

The four people were arrested after the messages were sent threatening to carry out killings at a kindergarten, a primary school and a comics fair and to place a bomb in a famous temple and inside an airplane.

In the case of the airplane, the message was sent directly to Japan Airlines and the threatened flight was forced to return to the airport after it had taken off.

Japan's public prosecutor's office had sought 10 years imprisonment for the accused.

Katayama had the authorities stymied for over a year and he was finally arrested in early 2013.

Before his arrest, he had sent a message to several media outlets in which he challenged the authorities to unmask him using a puzzle that led to them finding the file containing the virus that he had created.

Katayama had hidden the virus inside a memory card and placed it inside the collar of a cat on the street which the police discovered, leading to his arrest.

Katayama had earlier been sentenced in another case which was also related to sending threats through emails.