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. Rokuro created a short movie as ordered from Tamaki, supposedly shot from a hidden camera in his office. This shows how Tamaki talked to Ganta and Ganta supposedly "confessing" to all his crimes. The court acknowledged this as evidence and sentenced Ganta to death at Deadman Wonderland. 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 Deadman Wonderland and that the Red Man deliberatly framed Ganta for murder so that he could be taken to Deadman Wonderland.
After the closure of Deadman Wonderland, 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.