Former Hong Kong media mogul Jimmy Lai on Monday was found guilty of endangering national security in a landmark trial, a verdict that could see the 78-year-old locked up for life and fuel tensions between China and the U.S.

The city’s High Court on Monday convicted Lai on two counts of conspiring to collude with foreign forces — a crime punishable by life in prison under the Beijing-imposed National Security Law (NSL). The three-judge panel also found the creator of the now-defunct Apple Daily guilty of conspiring to publish seditious materials before his outspoken tabloid was forced to shutter.

Lai, who has spent more than 1,800 days in a maximum-security prison — most of it in solitary confinement — remained still upon hearing the verdict. Before he was led out of court back into custody, he waved and nodded to his family and supporters, with his hands pressed together.