A private elementary school on the outskirts of Tokyo remembered on Thursday those killed in a stabbing rampage one year ago at a crowded bus stop.

Caritas Elementary School officials laid flowers and prayed at the scene of the attack in Kawasaki on Thursday morning.

Hanako Kuribayashi, an 11-year-old student at the school, and Satoshi Oyama, a Foreign Ministry official and father of another girl, were killed in the attack. Eighteen others, mostly children waiting with their parents for a bus to the school, were also injured.

"We still live in deep sorrow. We will need to bear this lasting pain for a long time to come," the school's governing body said in a statement released Wednesday, in which it also voiced gratitude for the expressions of support it has received from across Japan.

After the attack, on the morning of May 28 last year, the school created two full-time counselor positions. The counselors were also available to speak to pupils over the phone during last year's summer holidays.

Yoshiki Tominaga, an expert on children's mental health care at the University of Hyogo, said children vary in the level of trauma and stress they suffer, which means the length of time needed for healing also differs.

"It is necessary for parents, teachers, counselors and psychiatrists to team up and provide care in the long term," the professor said.

The attacker, who wielded knives in both hands, was identified as 51-year-old Ryuichi Iwasaki. He killed himself at the scene shortly after the rampage.