Arnold mingled with Loyalist sympathizers in Philadelphia and married into one such family by wedding Peggy Shippen. She was a close friend of British Major John André and kept in contact with him when he became head of the British espionage system in New York. Many historians point to her as facilitating Arnold's plans to switch sides; he opened secret negotiations with André, and Peggy relayed the messages. The British promised £20,000 for the capture of West Point, a major American stronghold; Washington greatly admired Arnold and gave him command of that fort in July 1780. His scheme was to surrender the fort to the British, but it was exposed in September 1780 when Patriot militia captured André carrying papers which revealed the plot. Arnold escaped; André was hanged.