Two ex-managers of elevator maker Schindler Elevator K.K. pleaded not guilty at the start of their trial Monday in connection with an elevator accident that killed a 16-year-old high school boy in a Tokyo apartment complex in 2006.

Hitoshi Kamisasanuki, 61, and Ryuichi Harada, 44, told the Tokyo District Court they were not criminally negligent in managing the maintenance of its elevators.

The defendants stand accused of professional negligence resulting in the death of Hirosuke Ichikawa, a high school student, at the housing complex in Minato Ward where he lived. The youth was crushed to death when the elevator, with its doors open, suddenly moved as he was getting out.

Prosecutors said an abnormality in the ill-fated elevator's braking system had occurred before the lift came to an emergency stop in November 2004, and the managers failed to carry out the necessary checks and repairs or mention the incident to another firm that took over the maintenance inspections.

Schindler had been in charge of maintenance for the housing complex until March 2005.

In rebuffing the prosecutors' statement, the defense lawyers argued that the cause of the abnormality in the braking system has not been ascertained, denying the two were negligent, and noting that the braking system had been functioning normally as of November 2004.