At least 15 people were killed and about 45 wounded in a knife attack on Tuesday at a facility for the handicapped in a city just outside Tokyo.
Police said they responded to a call about 2:30 am from an employee saying something horrible was happening at the facility in the city of Sagamihara, west of Tokyo.
The attack began when the man, aged in his 20s, entered the facility in the early hours of the morning, police said, adding that he later appeared at a nearby police station and admitted to officers, "I did it."
According to National broadcaster NHK, 45 people had been injured and 28 people were seriously hurt.
NHK reported the suspect, 26, is a former employee at the facility, Tsukui Yamayuri-en.
Another broadcaster, NTV, said he broke into the facility by smashing a window with a hammer, and that he was upset because he had been fired, but that could not be independently confirmed.
Mass killings are relatively rare in Japan, which has extremely strict gun-control laws.
In 2008, seven people were killed by a man who slammed a truck into a crowd of people in central Tokyo's Akihabara electronics district and then stabbed passers-by.
Fourteen were injured in 2010 by an unemployed man who stabbed and beat up passengers on two public buses outside a Japanese train station in Ibaraki Prefecture, about 25 miles (40 kilometers) northeast of Tokyo.