The case arose from a complaint lodged before the CBI on April 27, 1995 by one Nirmal Kumar Bengani, who had approached Dhobi, then a parcel clerk at Hatia Railway Station, to book his motorcycle for transportation to Samastipur by train. The official booking charge was ₹203, but Dhobi allegedly demanded another ₹100, which Bengani alleged was a bribe.
Bengani had then approached the Central Bureau of Investigation (CBI), which laid a trap, planning an operation to catch Dhobi accepting a bribe the next day. The CBI treated a ₹100 currency note with phenolphthalein powder (a chemical used to detect contact with the currency note). Two independent witnesses accompanied Bengani to the parcel office while other CBI officials waited nearby.
According to the prosecution evidence, Dhobi first prepared the motorcycle booking receipt for ₹203 and then demanded the additional ₹100. Bengani handed him the treated note, which Dhobi allegedly placed in a drawer. Bengani then gave the pre-arranged signal, prompting the CBI team to enter the office.
The ₹100 note was recovered from the drawer and its number matched the number recorded before the trap. Dhobi’s right hand was also washed in a sodium carbonate solution, which turned pink. A forensic examination later confirmed the presence of phenolphthalein and sodium carbonate in the samples.