Nagano School Massacre

The Nagano school massacre is the event that started the Deadman Wonderland story. It takes place in the 4th state middle school of the Nagano prefecture. It starts with a regular day, with the students talking and taking their seats. But then, the Red Man appears outside the window while The Lullaby is playing. Ganta Igarashi is the only one who notices this Red Man. The Red Man uses his Branch of Sin and breakes the window. He enters the classroom and massacres everyone but Ganta. Ganta, who fainted during the massacre, wakes up and sees the Red Man approaching. The Red Man shoots a red diamond in Ganta's chest and Ganta faints again.

Aftermath
Ambulances arrive and the victims are given a burial. Ganta was put in a hospital and soon after that arrested and put charges for murder. Tamaki was appointed as his lawyer. Ganta couldn't prove his innocence and, taking account "numerous pieces of evidence", he was sentenced to death.

In the anime, this was slightly altered. Tamaki created a short movie supposedly shot from a hidden camera in his office. This shows how Tamaki talked to Ganta and Ganta confessing to all his crimes. The court acknowledged this as evidence and sentenced Ganta to death at DW. Also, what didn't happen in the manga, is that Mimi's father burst out in rage and attacked Ganta. He blamed him for his daughter's death and punched him in the ground. The guards removed him and Ganta was left alone, in despair.

Ganta is hereby sent to Deadman Wonderland. It was only later revealed that Tamaki was actually the Warden of DW and that the Red Man deliberatly framed Ganta for murder so that he could be taken to DW.

After the closure of DW, every Deadman's case was opened again and most of them were declared innocent. So was Ganta, due to fabrication of evidence and justification of his crimes in prison. Ganta was sent to an orphanage after that.