Tokyo prosecutors have decided not to indict five people in connection with an accident on a Tokyo subway line that killed five people and injured 64 others, informed sources said Monday.

According to the sources, the Tokyo District Public Prosecutor’s Office has begun preparations to explain its decision to the victims and victims’ families.

The fatal accident took place just after 9 a.m. on March 8, 2000, near Naka-Meguro Station on the Hibiya Line, which is operated by the Teito Rapid Transit Authority. The last carriage of an eight-car train derailed and sideswiped a train headed in the opposite direction on a parallel track.

Police sent papers on five people who were in charge of rail maintenance and management at the time to prosecutors on suspicion of professional negligence resulting in death and injury and endangering traffic passage.

The Metropolitan Police Department determined that the accident came about because the five did not take steps to repair warps and other problems with the rails. Investigations showed that 13 spots along the length of rail in question did not meet Teito’s standards as of November the previous year, and that improper maintenance work the next month left the surface of the rails ground down as much as five times the amount that had initially been planned. The five men in charge failed to check the rails and take proper steps to correct the situation, police alleged.

However, prosecutors have deemed that although there were mistakes in the repair and management of the rails, it was highly possible that other factors were also responsible for the accident, the sources said.

The then transport ministry, meanwhile, compiled an accident investigation report in which it said that in addition to the problems with the rails, various other factors, such as the load imbalance between the right and left wheels, also came into play.

It appears that prosecutors took this report into consideration in determining that the accident could not have been completely avoided if the five had properly maintained the rails, the sources said.