Although he did not participate in the Upper Canada Rebellion, Lett was charged in 1838 with the murder of Captain Edgeworth Ussher who had piloted the boats of Allan Napier MacNab during what would come to be known as the Caroline affair.
Moon, the three embarked on a raid in Cobourg to rob and kill Robert Henry and abduct Sheppard McCormick, a veteran of the attack on the Caroline.
[3] On or about 5 June 1840 in Oswego, New York, Lett attempted to burn the British steamship Great Britain while she was leaving the harbour.
Shortly before departure, a man identifying himself as "Bill Johnson" boarded the ship, placing a package containing three gunpowder-filled jars connected to a lit slow match at the door to the ladies' cabin.
[4] However, his luck in evading authorities on both sides of the border came to an end and that same month, he was captured in Buffalo, N.Y. and placed in solitary confinement in the Auburn prison.