Intelligence sources confirmed that ammonium nitrate and Nitrogen-Phosphorus-Potassium (NPK) used in the explosion were allegedly procured from Singhla around 20 days before the incident. His brother and business partner, Manoj, has remained underground since the arrest, officials and locals said.

Teams of the National Investigation Agency (NIA), Faridabad crime branch and other central units have widened the probe into Singhla, who operates Aggarwal Fertilizers' Agency with an extensive network in Punhana, Nagina, Taudu and Nuh. On Thursday, three doctors linked to Al-Falah University were detained, and on Friday the agencies swept through Pinangwan market, sealing Singhla's shops, godowns and associated businesses.

A district-level list of traders with a history of selling ammonium nitrate and NPK has been prepared and sent to the Superintendent of Police's office, officials said. Investigators also questioned Pinangwan sarpanch Manoj about Singhla's alleged role in "diverting chemicals" to Muzammil Ganaia, an associate of Dr Umar ul-Nabi. "We didn't suspect anything unusual in his business activities," he said.

Officials said investigative teams have visited Basai Meo and Biwa in Ferozpur Jhirka - areas surrounded by illegal mining belts where ammonium nitrate is "often traced… as they are used for explosion purposes on mountains," a senior Nuh police official said.

In Pinangwan, many fertilizer shops remained shut on Friday and Saturday amid surveillance. Traders who opened their stores denied knowledge of ammonium nitrate or NPK. "We only deal in Urea and DAP… We don't have CCTV cameras, and we usually don't check IDs," one retailer said. Another retailer claimed never to have procured NPK as "NPK is not used in mustard and wheat production… We have never sold NPK." However, Vrind Dev Arya, deputy director, agriculture department, said NPK is a common alternative to DAP and that three licensed wholesalers distribute the fertilizer annually.

In Sohna grain market, shops of longtime wholesalers Laxmi Seed Store and Madan Seed/Chemical Store were sealed and their owners detained. "Due to poor profit margins, often wholesalers indulge in selling fertilizers without proper registration and record keeping," a Gurugram-based dealer said. Another trader added, "It isn't possible to keep a record of every customer."

Gurugram deputy commissioner Ajay Kumar directed on Friday that only farmers registered on the Meri Phasal Mera Byora portal can purchase fertilizers. Similar initiatives may be introduced in Nuh. "Based on the state government's orders, farmers have been directed to complete their registrations to obtain fertilizers from cooperative and non-cooperative institutions," Kumar said.