A court in Bhopal on 27 March placed three of the accused responsible for the Bhopal-Ujjain passenger train blast in judicial custody till April 10.
The National Investigation Agency (NIA) had produced the accused before the court.
The Bhopal Anti-Terror Squad (ATS) handed over the case diary and other related documents to the NIA in March 15.
The police have not yet been able to establish any connection of the Bhopal-Ujjain passenger train blast with the ISIS.
"No connections have yet been established with the ISIS," Bhopal Inspector General (Law and Order) Makrand Devaskar said.
Earlier, Daljeet Chaudhary, the UP Additional Director General (ADG) of Police also said they had no evidence of any ISIS link, regarding the Lucknow terror stand-off, in which security forces gunned down a terrorist in an operation that lasted for nearly 10 hours in the thickly-populated Thakurganj area of Lucknow.
Devaskar also said they cannot establish a linkage between the two incidents as far as the current probe is concerned, however, two of the accused of the train blast were residents of Uttar Pradesh.
At least nine people were injured after the explosion took place in the train. The police arrested the three terrorists named mastermind Atif Muzaffar and Md. Danish - both residents of Kanpur, UP - and Syed Meer Hussain.