On 13 April, Brigadier General R.E.H. Dyer arrived from Jalandhar Cantonment, and virtually occupied the town as civil administration under Miles Irving, the Deputy Commissioner, had come to standstill. On Sunday, 13 April 1919, Dyer was convinced of a major insurrection and he banned all meetings; however, this notice was not widely disseminated.
That was the day of Baisakhi, the main Sikh festival, and many villagers had gathered in the Bagh. On hearing that a meeting had assembled at Jallianwala Bagh, Dyer went with ninety Sikh, Gurkha, Baluchi, Rajput troops from 2-9th Gurkhas, the 54th Sikhs and the 59th Sind Rifles.
Cruel Dyer continued the firing for about ten minutes, until the ammunition supply was almost exhausted; Dyer stated that 1,650 rounds had been fired, a number which seems to have been derived by counting empty cartridge cases picked up by the troops.
Official British Indian sources gave a figure of 379 identified dead, with approximately 1,200 wounded. The casualty number estimated by the Indian National Congress was more than 1,500, with approximately 1,000 dead.