Peter William Humphrey made the comments on Friday after his trial opened in Shanghai. They are the first such proceedings against foreign nationals. The Shanghai court reported the testimony on its official microblog.
Humphrey and his wife, Yingzeng Yu, are investigators who operated a small firm in Shanghai that helped corporate clients screen potential partners and employees and watch for embezzlement.
Their arrest last year coincided with a Chinese bribery investigation into GlaxoSmithKline. Glaxo said it hired Yu and Humphrey last year to investigate a security breach, but prosecutors have not indicated whether the two cases are linked.