Satoshi Uematsu (left) sits in the back seat of a police vehicle in Sagamihara, Kanagawa prefecture. AFP

A Japanese court Monday sentenced a former care home employee to hang for knifing to death 19 differently-abled people and injuring others four years ago in the deadliest mass attack in postwar Japan.

The Yokohama District Court convicted Satoshi Uematsu for the killings and for injuring 24 other residents and two caregivers at the Yamayuri-en residential buildings in July 2016.

During the investigation and trial, Uematsu repeatedly said he had no regrets and was trying to help the world by killing people he thought were burdens. Advocacy groups have said the suspect's views reflected a persistent prejudice in Japan against people with disabilities.

A police officer stands guard at the gate of Yamayuri-en, a facility for the differently-abled, in Sagamihara, Tokyo. File/AP

The trial focused on his mental state at the time of the crime. Chief judge Kiyoshi Aonuma dismissed defense requests to acquit him because he was mentally incompetent due to a marijuana overdose.

Prosecutors said Uematsu's criminal motive came from his biased personality and work experience at the home and not because of marijuana. They said Uematsu was fully mentally competent and should take responsibility for his crimes.

The killings mirrored a plot described in a letter Uematsu tried to give to a Parliament leader months prior to the attack. He quit his job at the Yamayuri-en facility after being confronted about the letter and was committed to psychiatric treatment, but he was released within two weeks, officials have said.

Uematsu, 30, also told medical staff and officials that he was influenced by the idea of Nazi Germany leader Adolf Hitler, whose killings of differently-abled people were seen as actions intended to improve the perceived master race.