HONG KONG (AP) — Hong Kong’s leader says the life sentence imposed by China on a 78-year-old U.S. citizen, who was also a Hong Kong permanent resident, on spying charges shows the city should “stay vigilant” to security risks. Chief Executive John Lee answered none of the lingering questions about why John Shing-Wan Leung was prosecuted. The sentence was announced Monday but neither the Hong Kong government nor the court in the eastern Chinese city of Suzhou that tried Leung have released details of the charges. The sentencing threatens to further exacerbate already strained ties between Beijing and Washington. A longtime Beijing loyalist, Lee has taken a hard line toward any signs of dissent in Hong Kong and oversaw a campaign that crushed the pro-democracy camp.