Updated 05/20/14 – 11:11 a.m.

CHICAGO (CBS) — Police believe they know what happened to a University of Illinois student who disappeared after he checked in for a flight at O’Hare International Airport, but never boarded the plane.

CBS 2’s Mike Puccinelli reports 19-year-old Hye Min Choi was last seen on Saturday, when he was scheduled to catch a flight from O’Hare to Greensboro, North Carolina.

The electrical engineering student, who also goes by the first name Joseph, had checked out of his dorm, took a bus to Chicago, and checked in his luggage on United Airlines flight 5892, but he never boarded the flight.

His mother was waiting for him in North Carolina, and quickly realized he wasn’t on the flight. Police said he did not re-book another flight with United.

Police in Chicago and Champaign have been searching for him ever since.

Chicago police think they know what happened. Police Supt. Garry McCarthy said there’s no evidence of foul play.

“There doesn’t appear to be any criminality involved. The young man apparently was having some problems in school. We have some leads on where he may be. It appears that he may or may not have wanted to go home,” McCarthy said. “It happens once in a while, by the way; more frequently than you know.”

Sources said Choi might have been upset over his final exams, but authorities would not confirm that.

His mother flew to Chicago and has been reviewing surveillance video tapes with police.

Choi is described as a 5-foot-6, 100-pound, Asian Pacific Islander, with brown eyes, black hair and a medium complexion. He has a scar on his right eyelid.

The university has been notified of the missing student, police said.

Anyone with information on Choi’s whereabouts should call Area North detectives at (312) 744-8266.

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