Why was tzar Nicholas and his family murdered

As a reaction to the seizure of power by the Bolsheviks in Russia, a counterrevolutionary army, the "White" army of Gen. Kornilov was formed with the purpose to remove them from power and also make Russia rejoin World War One, which it had got out of with by signing the Treaty of Brest-Litovsk with Germany. Fearing that for legitimacy the counterrevolutionaries may want to restore tsarist rule, the Bolsheviks murdered the former Czar Nicholas II and his family that they had been holding hostage in Ekaterinburg.