The 85 Indian troopers were court martialled in Meerut for refusing to use new cartridges rumored to contain cow and pig fat. On May 10th, the troopers stormed the jail and released their comrades, and civilians joined in killing 50 Europeans. The revolt quickly spread due to political, social, religious, economic and administrative grievances under the British East India Company's rule. Key centers of revolt included Meerut, Delhi, Kanpur and Jhansi. The revolt was suppressed by July 1858, and led to control of India being transferred to the British Crown and more involvement of Indians in administration.