Bihar train derailment

On June 6, 1981, a train crashed in Bihar, India. It was carrying more than 800 passengers, traveling between Mansi railway station and Saharsa railway station. It derailed and fell into the River Bagmati while it was crossing the bridge over the river. 
Casualties.
Five days after the accident only 200 out of 800 passengers had been recovered as dead bodies with hundreds more people missing. The missing passengers were thought to have been washed away by the River Bagmati. Total deaths were listed as 500-800. This derailment stands in 4th place in the worst railway accidents by death toll in the world.
Reasons.
Many reasons were given for this railway derailment accident. They were: