Those killed in Sunday’s accident were traveling in three vehicles in the 4.7-kilometer (3-mile) long Sasago Tunnel about 80 kilometers (50 miles) west of Tokyo. The tunnel, on a highway that links the capital to central Japan, opened in 1977.
About a dozen uniformed police were shown on television entering the headquarters of Central Japan Expressway Co. early Tuesday, toting cardboard and plastic boxes.
“Yes they are searching our offices here. We will be fully cooperating with them,” said Osamu Funahashi, an official at the government-owned company.
The transport ministry has ordered inspections on 49 other tunnels around the country.