Question: who was the last person executed for treason
[{'answer': 'William Bruce Mumford', 'provenance': [{'wikipedia_id': '2111515', 'title': 'List of people convicted of treason', 'start_paragraph_id': 179, 'start_character': 12, 'end_paragraph_id': 179, 'end_character': 33, 'bleu_score': 1.0, 'section': 'Section::::United States.\n'}]}]