The case involves recovery of 22 AK-47 rifles in Munger smuggled from the Central Ordnance Depot in Jabalpur in September 2018.
According to an NIA official associated with the probe, the agency has identified several gun runners and Maoists in Bihar, who might have bought the assault rifles between 2012 to 2018 from Purushottam Lal Rajak, a retired employee of the Ordnance Depot.
Rajak was arrested by Munger Police in September 2018 and confessed to transporting 70 Ak-47 assault rifles and spare parts to criminals in Munger.
The weapon smuggling first came to light on August 28, 2018, when Munger police arrested Mohammad Imran with three AK-47 rifles and recovered three more weapons from an arms dealer, Shamsher Alam.
Following their interrogation, 12 more AK-47 rifles were recovered from a well in Munger's Mirzapur village on September 28, 2018. The police then arrested a retired army jawan, Niyazur Rehman, from New Jalpaiguri in West Bengal.
With the expanding sweep of the case, the NIA in October 2018 took over the case from the Bihar Police on the Union Home Ministry's orders.
After Rajak's arrest, raids were carried out last month at over 11 locations in Uttar Pradesh and at the residences of Lok Janshakti Party (LJP) leader Hulas Pande in Bihar's Bhojpur, Rohtas and Patna districts.
One rifle with cartridges, Rs 29 lakh cash, four laptops, five hard disks, 12 pen drives, 12 mobile phones, a computer and incriminating documents, including cash receipts and bank details were recovered in the raids.
The NIA official said Hulas appeared on the agency's radar due to his sand mining business in Rohtas and Bhojpur, where Maoists once had a strong presence.
Another senior official associated with the probe said the agency had also got leads about Pande's transportation business. "One of Pande's firms worked as a transporter for the Bihar State Food Corporation (BSFC) and there also some cases of irregularities against it," he said.
His elder brother, Sunil Pande, a former JD-U MLA from Bhojpur's Piro area, is an old associate of the now jailed criminal-turned-politician Mohammad Shahabuddin. Sunil Pande was also one of the founder members of Bihar's upper caste militia Ranveer Sena and in 1994 waved an AK-47 rifle during a Ranveer Sena meeting in Bhojpur.
Associates of the Pande brothers are now under the NIA scanner. "Pande brothers' Maoists links cannot be ignored but we are collecting evidence about how the guns were bought from Rajak or his associates. We are also trying to identify persons who worked as gunrunners for Rajak in Bihar," the official said.
The NIA has so far arrested 15 accused in the case. The agency has also chargesheeted nine accused, including the racket kingpin Rajak, Suresh Thakur, Imran Alam and Rahman.
(Anand Singh can be contacted at anand.s@.in)
( With inputs from IANS )