Tomohiro Kato pleaded guilty Thursday to murdering seven people and injuring 10 in Tokyo’s popular Akihabara electronics district in June 2008.

With the guilty plea, the trial at the Tokyo District Court will now turn on whether the 27-year-old’s mental condition at the time of the massacre was stable enough to assign criminal responsibility. This determination will influence his sentence, which could be the death penalty.

“First of all, I would like to apologize to those who have passed away, to those who were injured and to their families,” Kato said as presiding Judge Hiroaki Murayama asked him to enter his plea.

“Although there are some parts that I have no memory of, I admit that I committed (the crime) and that I am the culprit,” Kato read from a memo he had prepared in advance.

With trimmed hair and dressed in a black suit with white shirt, the pale-looking Kato bowed to the gallery when he first entered the courtroom. Several survivors and relatives of the victims were among the audience.

Kato stands accused of plowing a rented truck into a crowd of pedestrians at around noon on June 8, 2008, then getting out of the vehicle and going on a stabbing rampage.

Three died from the impact of the truck and two were injured. Wielding a dagger, Kato then stabbed four people to death and knifed another eight who survived. Most of the victims had been shopping.

In their opening statement, the prosecutors said they will establish that Kato was criminally responsible for his actions.

Kato, a temporary worker at a car repair factory in Shizuoka Prefecture at the time, had been constantly posting messages on a cell phone bulletin board.

The prosecutors said Kato had a strong sense of being ignored by society and the bulletin board provided his only escape.

When people began to criticize his entries, the prosecutors argued, Kato felt betrayed and could not forgive them.

They said that a few days before the rampage, he became incensed when no one replied with kind words to a post saying he was upset about the disappearance of his work clothes at the factory.

After searching for his clothes in vain, Kato took it as a message from his employer to quit the factory, the prosecutors said.

Kato continued to write on the bulletin board, entering his moves leading up to the attack, including purchasing of a dagger and other knives, renting a 2-ton truck and that he was in Akihabara and was about to proceed with his plan.

Kato ran a red light and barreled into an intersection crowded with pedestrians. The area was mostly closed to traffic because it was a Sunday.

The prosecutors said a psychiatric test performed before Kato was indicted indicated he did not have any mental problems and was criminally responsible, and they will prove their case during the trial.

Kato’s lawyers asked the court to focus carefully on his upbringing and how his ways of thinking developed.

They also asked the court to pay close attention to what the online bulletin board meant to their client.

“It is impossible to understand his motives without understanding what the bulletin board meant to him,” said the lawyer who made the opening statement for the defense.