A former top bureaucrat at the farm ministry admitted to killing his socially reclusive son on Wednesday, the first day of his high-profile trial in Tokyo.

Hideaki Kumazawa, 76, a former vice minister for agriculture, forestry and fisheries, is on trial for stabbing his 44-year-old son Eiichiro in the neck multiple times around 3:15 p.m. on June 1, causing his death from massive blood loss, according to indictment.

Prosecutors said the defendant feared for his safety before deciding to kill his son who had displayed violent behavior in the family home ever since he was bullied at a famous private junior high school.

After graduating from high school, Kumazawa moved his son into his own home in the Mejiro area of Tokyo but he moved back to his parents' home in the capital's Nerima Ward a week before the incident, prosecutors said.

A day after Eiichiro returned to his parents' home, he assaulted his father for bringing up the issue of some garbage left at the Mejiro residence. After that, Kumazawa and his wife moved to live exclusively in the second floor of their home.

The defendant decided to kill his son and left a note saying, "I think there is no other way," prosecutors said. After the incident, he called police to report the stabbing.

The defense team said Wednesday that Eiichiro had previously been diagnosed with schizophrenia and Asperger's syndrome, adding the defendant "desperately supported and cared for his eldest son."

"He was suddenly compelled to kill him, thinking he would be killed otherwise," his lawyer said.

At the time of his arrest, investigative sources said the defendant explained his actions were prompted by a fear his son might harm children in an incident similar to a mass stabbing that occurred in Kawasaki a few days earlier.

But neither prosecutors nor the defense team mentioned the knife attack on a group of elementary school children and parents that left two dead and injured more than a dozen others west of Tokyo. It was allegedly carried out by a 51-year-old recluse who lived with his elderly uncle and aunt.

(File photo)

At the end of the hearing at the Tokyo District Court, prosecutors called on the group of citizen judges to listen to the evidence-based facts presented in the case.

Kumazawa joined the forerunner to the farm ministry in 1967 and became vice minister in 2001. He stepped down the following year amid criticism over the ministry's handling of a mad cow disease outbreak.

He went on to serve as Japan's ambassador to the Czech Republic from 2005 to 2008.

The case has drawn much public attention due to the large number of social recluses, known as "hikikomori," aged 40 to 64 in Japan. The government estimates there to be 613,000 across the country.

As the parents of hikikomori age, the so-called "8050 problem" has emerged as parents in their 80s and their children in their 50s experience financial struggles.

Experts on hikikomori regularly call on family members to consult with specialized institutions or support groups as many parents tend to blame themselves or choose to hide their problems due to concerns about the associated social stigma.

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