British Government had killed a large no. of INA soldiers in the Jhikargacha and the Neelganj camps. There are collective memories from the local population who had been witnesses to large scale firings during the midnight. According to the eyewitness testimony a large no. of INA soldiers who were identified as "blacks" by the British Government were killed on the night of 25th September 1946, and their bodies were burnt. Machine gun fires were heard throughout the night and in the morning villagers and local residents could see piles of burnt and unburnt bodies. Many bodies were dumped in the local river whose water turned red. While commenting on this incident, Amrita Bazar Patrika reported that Nehru had said that there was a firing in Neelganj camp and only 5 people had died. Till date no serious research has been done on this subject by the eminent historians.
An account of the slaughter is given here -
Writes Kanailal Basu in his book Netaji Rediscovered, "File relating to the Jhikargacha camp, available in the National Archives, contains documents showing a report sent by the Eastern Command to the General HQ, informing them about the killing of INA prisoners. There were about 1580 prisoners in Jhikargacha camp." None of them were released. So it is presumed that all were killed in one night's covert operation that left no witness alive.
Details provided in https://www.netajisubhasbose.org/