<P> Bank of Delhi was attacked by mortar and gunfire </P> <P> An eagerly awaited heavy siege train joined the besieging force, and from 7 September, the siege guns battered breaches in the walls and silenced the rebels' artillery . An attempt to storm the city through the breaches and the Kashmiri Gate was launched on 14 September . The attackers gained a foothold within the city but suffered heavy casualties, including John Nicholson . The British commander wished to withdraw, but was persuaded to hold on by his junior officers . After a week of street fighting, the British reached the Red Fort . Bahadur Shah Zafar had already fled to Humayun's tomb . The British had retaken the city . </P> <P> The troops of the besieging force proceeded to loot and pillage the city . A large number of the citizens were killed in retaliation for the Europeans and Indian civilians that had been slaughtered by the rebels . During the street fighting, artillery was set up city's main mosque, neighbourhoods within range were bombarded; the homes of the Muslim nobility that contained innumerable cultural, artistic, literary and monetary riches destroyed . </P> <P> The British soon arrested Bahadur Shah, and the next day the British agent William Hodson had his sons Mirza Mughal, Mirza Khazir Sultan, and grandson Mirza Abu Bakr shot under his own authority at the Khooni Darwaza (the bloody gate) near Delhi Gate . On hearing the news Zafar reacted with shocked silence while his wife Zinat Mahal was content as she believed her son was now Zafar's heir . Shortly after the fall of Delhi, the victorious attackers organised a column that relieved another besieged Company force in Agra, and then pressed on to Cawnpore, which had also recently been retaken . This gave the Company forces a continuous, although still tenuous, line of communication from the east to west of India . </P>

Describe how the sepoy mutiny transformed into a rebellion