New Delhi/Patna, July 12 : A team of National Investigation Agency (NIA) on Monday arrived in Bihar's Darbhanga railway station to probe the case of an explosion in a parcel bag on June 17 and questioned several people. According to NIA sources, a six-member team of the anti-terror probe agency arrived at Darbhanga station and met with several officials of the Government Rail Police (GRP), Railway Protection Force (RPF) and the parcel officials. The source said that the agency team spoke to the officials of the railways in length about the explosion on June 17. The NIA has arrested four persons in connection with the case. They included -- Imran Malik and Mohammad Nasir Khan (both brothers) and members of the Lashkar-e-Taiba (LeT) from Hyderabad arrested on June 30; Mohammad Salim Ahmed aka Haji Salim and Kafil aka Kafeel, both residents of Uttar Pradesh's Kairana arrested on July 2 from Kairana. The agency had on last Wednesday said that preliminary investigation had revealed a trans-national conspiracy hatched by top operatives of the proscribed terror outfit LeT to execute terror acts across India and cause large-scale damage to life and property. The NIA had said that acting under the directions of Pakistan-based handlers of Lashkar, Khan and Malik had fabricated an incendiary IED and packed it in a parcel of cloth and booked the same in a long-distance train from Secunderabad to Darbhanga. The anti-terror probe agency also pointed out that this was aimed at causing an explosion and fire in a "running passenger train", resulting in huge loss of lives and property. /IANS