Despite the presence of Scott's army just outside of Mexico City, the Mexican and American delegations remained far apart on terms; Mexico was only willing to yield portions of Alta California, and refused to accept the Rio Grande as its northern border. While negotiations continued, Scott faced a difficult issue in the disposition of 72 members of Saint Patrick's Battalion who had deserted from the U.S. Army and were captured while fighting for Mexico. All 72 were court-martialed and sentenced to death. Under pressure from some Mexican leaders, and personally feeling that the death penalty was an unjust punishment for some defendants, Scott spared 20, but the rest were executed. In early September, negotiations between Trist and the Mexican government broke down, and Scott exercised his right to end the truce. In the subsequent Battle for Mexico City, Scott launched an attack from the west of the city, capturing the key fortress of Chapultepec on September 13. Santa Anna retreated from the city after the fall of Chapultepec, and Scott accepted the surrender of the remaining Mexican forces early on the 14th.