Ramalingayapalli, Dec 23: A day after the Bangalore Express derailed in Andhra Pradesh killing 20 people and injuring 87, a controversy has erupted over the cause of the accident with railways claiming it to be an act of sabotage by the naxalites and police attributing it to "track fault". "It is a planned act of a naxalite group". The track was cut using hacksaw blades and the damaged portion was covered with a piece of cloth, said South Central Railway General Manager S M Singla.