A 20-year-old California man has been charged with assault and interfering with a flight crew in an alleged assault on a flight attendant on a cross-country American Airlines flight, federal prosecutors said Monday.

Details of the allegations against Brian Hsu of Irvine were not immediately available. The case was listed as sealed.

It is not known if Hsu has an attorney. He was expected to appear in federal court in California’s Central District later Monday, the U.S. Attorney’s Office for Colorado said in a press release.

Flight 976 from John F. Kennedy International Airport in New York to John Wayne Airport in Santa Ana, California was diverted to Denver on Wednesday because of the incident, which was investigated by the FBI and did not immediately result in an arrest.

The assault comes amid a surge in unruly airline passengers this year, who sometimes become violent.

Passenger Mackenzie Rose told CBS Los Angeles  that the flight attendant was assaulted about halfway through the trip, when the plane was over Ohio.

At the time, Fort Worth, Texas-based American said the passenger, not publicly identified then, would be banned from all future flights and called for his prosecution. “This behavior must stop,” it said.

Associated Press