School authorities were warned three years ago about the substandard concrete wall that collapsed onto a 9-year-old girl and killed her following Monday’s earthquake in the Osaka area, the local education board said.

In a related development Friday, the local education board in quake-hit Takatsuki, Osaka Prefecture, also said it had discovered another 15 public schools where substandard concrete walls on their premises could pose a danger to students in the event of powerful earthquakes.

According to the board, disaster prevention adviser Ryoichi Yoshida informed them and the school in 2015 about the danger of the high wall, which was made from concrete blocks, around the swimming pool of Juei Elementary School in Takatsuki.

Rina Miyake was on her way to school on Monday when the magnitude 6.1 quake struck, and was crushed to death after the wall collapsed.

The education board told a news conference that following the warning it checked the wall, in February 2016. After visually assessing the structure and striking it with a stick, board staff judged it to be safe. But the board said the two officials who inspected the wall did not have any architectural qualifications. While apologizing for its failure to prevent the death, the board said it had not viewed the wall as being in violation of the law and believed that it posed no problem as no cracks were found.

But Yoshida said concrete experts should have assessed the wall’s safety, and expressed skepticism about the board’s handling of the matter. Yoshida, who gives disaster lectures across Japan, made a speech on disaster prevention at the elementary school on Nov. 2, 2015, after assessing danger points on routes taken by pupils walking to school. He told the school’s vice principal at the time about the potential risk of the concrete wall.

To follow up about the danger, he sent an email to the school on Dec. 7 the same year and attached data to support his claim. He warned the school that concrete walls built before the 1981 revision to building standards laws need particular attention. According to the education board, Yoshida’s advice was not shared within the organization.

In a separate news conference, also Friday, education minister Yoshimasa Hayashi commented on the revelations, saying, “If safety measures were not taken despite warnings, we need to thoroughly verify (the response).”

The wall, which reached as high as about 3.5 meters including a 1.9-meter foundation, was made of blocks stacked higher than legal standards permit, with insufficient reinforcement. Local police are looking at the death as a possible case of professional negligence.

Regarding the 15 additional schools where substandard concrete walls have been found, nine were elementary schools and six were junior high schools, the board said, adding that the walls will be removed in a few weeks. The city conducted an emergency survey of concrete walls this week following the death at Juei Elementary School.

The 15 schools are among the 59 public elementary and junior high schools in Takatsuki.