Suspected brake failure could have led to the rail mishap in Rae Bareli, according to sources and eyewitnesses, although Railways have maintained that prima-facie cause of the derailment was overshooting of the signal by the loco driver. Sources said the driver apparently applied the brake but the train did not stop pointing suspicion towards the failure of the braking system. Railway Minister Suresh Prabhu has ordered an inquiry into the incident by the Commissioner Railway Safety (CRS) of Northern Zone. "The real cause of the mishap would be known only after the inquiry, but it seems the driver apparently applied the brake but could not stop the train," sources said.