Why was Nicholas II arrested in 1917 during the Russian revolution?

When the February Revolution broke out it was clear that Nicholas II had lost control of the country and could not stop the revolution that was beginning. He was convinced he had to abdicate in order to preserve order. The new Provisional Government took him into custody to assure that he would not be able to take back the throne he had just given up or that no one else could put him back on it.

The plan had been to send him in exile to England; but the Bolsheviks staged their coup in the October Revolution and toppled the Provisional Government. The Bolsheviks then took Nicholas into their custody and quickly decided it would not be a good idea to allow the former Tsar to live in exile in Another Country where he might gain support for restoration. When the Russian Civil War broke out it was clear to the Bolsheviks that some of the forces fighting against them would try to put Nicholas back on the throne, so the Bolsheviks murdered him and his whole family in July 1918.