Answer by taking a quote from the following article:

Sri Aurobindo (Bengali: [Sri Orobindo]) (born Aurobindo Ghose; 15 August 1872 - 5 December 1950) was an Indian philosopher, yogi, guru, poet, and nationalist. He joined the Indian movement for independence from British rule, for a while was one of its influential leaders and then became a spiritual reformer, introducing his visions on human progress and spiritual evolution. Aurobindo studied for the Indian Civil Service at King's College, Cambridge, England. After returning to India he took up various civil service works under the maharaja of the princely state of Baroda and became increasingly involved in nationalist politics and the nascent revolutionary movement in Bengal.

In July 1905 then Viceroy of India, Lord Curzon, partitioned Bengal. This sparked an outburst of public anger against the British, leading to civil unrest and a nationalist campaign by groups of revolutionaries, who included Aurobindo. In 1908, Khudiram Bose and Prafulla Chaki attempted to kill Magistrate Kingsford, a judge known for handing down particularly severe sentences against nationalists. However, the bomb thrown at his horse carriage missed its target and instead landed in another carriage and killed two British women, the wife and daughter of barrister Pringle Kennedy. Aurobindo was also arrested on charges of planning and overseeing the attack and imprisoned in solitary confinement in Alipore Jail. The trial of the Alipore Bomb Case lasted for a year, but eventually he was acquitted on May 6, 1909. His defence counsel was Chittaranjan Das.  During this period in the Jail, his view of life was radically changed due to spiritual experiences and realizations. Consequently, his aim went far beyond the service and liberation of the country.  Aurobindo said he was "visited" by Vivekananda in the Alipore Jail: "It is a fact that I was hearing constantly the voice of Vivekananda speaking to me for a fortnight in the jail in my solitary meditation and felt his presence."  In his autobiographical notes, Aurobindo said he felt a vast sense of calmness when he first came back to India. He could not explain this and continued to have various such experiences from time to time. He knew nothing of yoga at that time and started his practise of it without a teacher, except for some rules that he learned from Ganganath, a friend who was a disciple of Brahmananda. In 1907, Barin introduced Aurobindo to Vishnu Bhaskar Lele, a Maharashtrian yogi. Aurobindo was influenced by the guidance he got from the yogi, who had instructed Aurobindo to depend on an inner guide and any kind of external guru or guidance would not be required.  In 1910 Aurobindo withdrew himself from all political activities and went into hiding at Chandannagar in the house of Motilal Roy, while the British were trying to prosecute him for sedition on the basis of a signed article titled 'To My Countrymen', published in Karmayogin. As Aurobindo disappeared from view, the warrant was held back and the prosecution postponed. Aurobindo manoeuvred the police into open action and a warrant was issued on 4 April 1910, but the warrant could not be executed because on that date he had reached Pondicherry, then a French colony. The warrant against Aurobindo was withdrawn.

What stopped them?
However, the bomb thrown at his horse carriage missed its target and instead landed in another carriage and killed two British women,