NEW DELHI: As NIA awaits the go-ahead from the home ministry to take over probe into the alleged ISI-backed conspiracy to trigger train derailments by planting IEDs on tracks, sources said two WhatsApp audio clips had been recovered from the phone of an arrested accused, in which two suspects can be heard discussing the November 20 derailment of Indore-Patna Express near Kanpur."While the claim made by Moti Paswan, one of three accused arrested in Bihar's East Champaran district, stating that he was involved in planting explosives to derail the Indore-Patna Express and the Ajmer-Sealdah express near Kanpur was seen as rather circumspect as the probe conducted by the railways had not picked any forensic evidence of explosives, the recovery of technical evidence in the form of audio clips has made it imperative to take his disclosure seriously and thoroughly investigate the terror angle," said a police officer.The conversation in the audio clip took place after the Kanpur derailment that killed 151 people, said a source.Sources said NIA may probe at least three related cases - the failed attempt to cause a train derailment at Ghorasahan in October last year; the killing of two suspects who planted the bomb at Ghorasahan by Nepal-based handler Brij Kishore Giri; and the alleged terror angle to the derailment of Indore-Patna Express and Ajmer-Sealdah Express near Kanpur last year. For the Kanpur derailment case, NIA plans to not only interrogate Paswan, who made the sensational disclosure regarding ISI plot to target trains in India while being questioned in a murder case, but also thoroughly verify his claim by taking him to the accident site to reconstruct the bomb-planting, establishing his travel from Motihari to Kanpur, and looking for any trail of payments made to the accused for planting the bomb.The NIA sleuths may also visit Nepal to question the three suspects arrested there for murder of two criminals who had planted the bomb at Ghorasahan but failed to detonate it in October last year. Sources said with the three key suspects already under arrest in Nepal, the probe may become complicated as NIA would either have to move a request for their extradition or travel to Nepal to interrogate them.NIA will also seek custody of the accused arrested in Bihar and Delhi.