A Japanese man accused of stabbing 19 disabled people to death pleaded not guilty due to mental illness, in a dramatic trial interrupted when he seemed to put something in his mouth, struggled with court officials and lay on the floor writhing.

Key points: Mr Uematsu's lawyer claimed abuse of marijuana led to his client's mental illness

Mr Uematsu's lawyer claimed abuse of marijuana led to his client's mental illness His violence sparked debate about the national stigma surrounding disability

His violence sparked debate about the national stigma surrounding disability Violent crimes are rare in Japan due to strict gun control

Satoshi Uematsu, 29, a former care worker, is accused of killing 19 people and wounding 26 in a care centre in 2016, in one of post-war Japan's worst mass killings.

He was removed from the court following the disruptions and did not return when the trial resumed.

Before the interruption, his lawyer said Mr Uematsu acknowledged details of the indictment were true, but he has a psychiatric disorder that led to diminished capacity at the time of the incident.

"Mr Uematsu had a psychiatric disability and, as a result, he was not mentally competent," said the lawyer.

A calm-looking Mr Uematsu, wearing a navy blue suit, white shirt and tie, with his hair in a long pony tail, bowed slightly as he entered the courtroom, before he made motions as if to put something in his mouth, Japanese media said.

Mr Uematsu was arrested after the 2016 killings at a care facility in the city of Sagamihara ( Reuters: Issei Kato )

A Reuters witness saw him struggling with uniformed court officials, writhing on the floor as three officials held him down, before the hearing was abruptly adjourned for about an hour.

Once the hearing resumed without Mr Uematsu in attendance, one of his lawyers said his abuse of marijuana had led to mental illness.

"This has turned him into a different person. As a result, this incident took place," his lawyer said.

But a prosecutor told the court any potential sentence would have to take into consideration the brutality and scale of the crime, noting that Mr Uematsu had stabbed many victims in the neck.

"[Mr Uematsu] had the capacity to tell good from bad, and capacity to control his conduct as well," the prosecutor said.

"We will prove he was completely responsible for what he did."

'I want people to know who she was'

Police raided Mr Uematsu's home in 2016 to gather evidence. ( Reuters: Issei Kato )

The July 2016 killings at the facility in Sagamihara, southwest of Tokyo, where Mr Uematsu had once worked, shocked the country, as violent crime is rare due to strict gun control.

Local and international media has kept a keen interest on Mr Uematsu since 2016, including when police searched Mr Uematsu's house to gather evidence for his trial.

Interest in the trial was intense, with nearly 2,000 people lining up in the cold rain for 26 viewing seats, and broadcast trucks lined the streets in front of the courthouse.

The violence also sparked debate about the need for change in a society where people with disabilities can still suffer stigma and shame, a situation highlighted by the fact that the families of most of those killed have not revealed their names.

On Wednesday (local time), family members of the victims watched from a screened off area of the courtroom.

One woman told Japan's national broadcaster NHK, that the trial prompted her to change her mind about concealing the name of her daughter who was 19 when she was killed.

Photos of the young woman, who was autistic and unable to speak, show her smiling shyly.

The photo was taken by her mother soon after she entered the care home, just months before she was killed.

"She loved music, she lived as energetically as she could," her mother wrote in the statement quoted by NHK, saying she last saw her daughter two days before her death.

"Her name was Miho. I want that public as proof that she existed. I want people to know who she was."

Reuters