Photo/Illutration Two brothers died after falling from the seventh floor of this apartment building in Nagoya on March 24. (Kohei Higashitani)

NAGOYA—Twin toddlers who fell from a seventh-floor apartment likely climbed on a shelf near a window, slid it open and then plunged to their deaths, investigative sources said.

The 2-year-old brothers, Toya and Yuya Mabe, were confirmed dead at a hospital on March 24 with broken skulls, Aichi prefectural police said.

They were living in a room on the seventh floor of a nine-story apartment building.

The unit has a sliding window about 120 centimeters tall and wide that faces a parking lot. A horizontal bar had been installed 30 cm above the bottom of the window as a safety measure.

An 80-cm-tall shelf that reaches the bottom of the window was located beneath the right side of the window. The brothers were also 80 cm high, according to police.

The shelf has parts that the children could have used to put their feet on when they climbed up.

Their parents told police that they were home when their children fell.

“I locked the window,” the mother was quoted as saying. “I was in another room and looked away for a few minutes.”

Both sides of the window can slide open. But its right side was fixed with a stopper to prevent it from moving.

However, the left side, which was open when the toddlers were found on the ground, did not have a stopper.

A man made an emergency call to police around 3:55 p.m. on March 24, saying, “I saw a child on the ground in a parking lot, and then another child has just fallen down from above.”