However, this did little to end the discontent; in 1768, a riot started in Boston when the authorities seized the sloop "Liberty" on suspicion of smuggling. Tensions escalated further in March 1770 when British troops fired on rock-throwing civilians, killing five in what became known as the Boston Massacre. The Massacre coincided with the partial repeal of the Townshend Acts by the Tory-based North Ministry, which came to power in January 1770 and remained in office until 1781. North insisted on retaining duty on tea to enshrine Parliament's right to tax the colonies; the amount was minor, but ignored the fact it was that very principle Americans objected to.