Short answers, pulled from the story.
Nathuram Godse, a right-wing Hindu nationalist from Pune and former member of the Rashtriya Swayamsevak Sangh, assassinated Gandhi on the 30th of January 1948. Godse believed Gandhi's influence over the Indian government bypassed democratic will and that Gandhi's fasts and teachings had caused suffering to Hindus while facilitating Pakistan's demands.
Gandhi was assassinated on the 30th of January 1948 at Birla House, a large mansion on what was then Albuquerque Road in south-central New Delhi. He was shot at approximately 5:17 p.m. while walking to his evening prayer meeting on the raised lawn behind the mansion, and was pronounced dead at around 5:40 p.m.
Godse used a Beretta M1934 pistol, which he and his collaborator Narayan Apte had purchased in January 1948. He fired three bullets into Gandhi at point-blank range.
Godse was seized at the scene, tried at Delhi's Red Fort beginning on the 27th of May 1948, and sentenced to death on the 8th of November 1949. Pleas for commutation by Gandhi's sons were refused by Prime Minister Nehru, Deputy Prime Minister Patel, and Governor-General Chakravarti Rajagopalachari. Godse was hanged at Ambala Gaol on the 15th of November 1949.
More than two million people joined Gandhi's funeral procession. It stretched five miles and took over five hours to travel from Birla House to Raj Ghat, where Gandhi was cremated on a funeral pyre.
The RSS was banned on the 4th of February 1948 and approximately twenty thousand of its members were arrested in the following months. The case for declaring India a Hindu state effectively collapsed because of the association between Hindu nationalism and the killing, and secular values were reestablished in the new republic.