Searches were carried out at the office of Rikuentai bus company in Inzai, Chiba prefecture, as well as the home of the company's president, Yumihide Hariu, on suspicion of negligent driving resulting in death and injury, Kyodo News reported.
Police confiscated Rikuentai's daily operations report and working regulations to determine whether the weekend accident was caused by driver fatigue after the driver of the bus, Kazan Kono, told police he fell asleep at the wheel. Kono was hospitalized with serious injuries and is expected to recover, police said.
The bus left Kanazawa, Ishikawa prefecture, around 10 p.m. Saturday and was heading for Tokyo Disneyland when it crashed into a guard wall on the Kanetsu Expressway in Fujioka at 4:40 a.m. Sunday, Kyodo News reported.
Kono called Hariu from the scene to report the crash.
"I'm sorry. I caused an accident and crashed into a wall," Hariu quoted Kono as saying.
Police said they would question Kono on suspicion of manslaughter resulting from negligent driving.
Bus industry officials say the crash was a result of cost-cutting and excessive competition in the industry, The Mainichi reported.
"Anyone who has five buses with one supervisor can now enter the market thanks to the deregulation, which has triggered excessive price competition and severe labor conditions for drivers," said a senior official with a bus company in Ishikawa prefecture.
A 52-year-old bus driver agreed, saying drivers often take on exhausting routes to make more money as fares get cheaper.
"Our salaries have also been halved compared to a decade ago. In order to survive, bus drivers have no choice but to undertake assignments under adverse conditions. Some may drive on very tight schedules," he said.