Relatives of victims of a fatal bus crash on Wednesday marked the ninth anniversary of the accident that claimed the lives of 13 passengers and two drivers in Karuizawa, Nagano Prefecture, on Jan 15, 2016.

The group also included representatives of bus company ESP, as well as local government officials. They placed flowers at a monument near the site of the accident and prayed for the deceased.

ESP president Misaku Takahashi said: "As time passes, I feel more and more sorry."

Takahashi and two other employees of the bus company were charged with professional negligence resulting in death and injury in connection with the accident, and were sentenced to three years in prison by the Nagano District Court in June of last year, but are appealing the verdict.

The charter bus from Tokyo careened off a road at 2 a.m. while traveling downhill in Karuizawa, killing 13 students, the 65-year-old driver and a relief driver. Twenty-six other students were injured.

A transport ministry commission that investigated the accident pinned the blame squarely on the driver, saying he lost control of the bus after allowing it to gain speed by driving downhill with hardly any application of the brakes.

Based on its findings from a simulated crash and roadside camera footage, the commission concluded that the bus was traveling downhill for about one kilometer with hardly any engine or foot braking. The bus eventually went off the road after failing to negotiate a left curve at a speed of 95 km per hour, far above the speed limit in the area.

The commission said in a report that the Tokyo-based bus operator increased the risk of accidents involving its drivers by not ordering them to take regular health checks or conducting roll calls before they set off.

While the commission called for the transport ministry to increase its checks on bus operators, the ministry has already toughened its supervision of charter bus operators, now requiring them to renew their business permits every five years.