Coibion was last seen at the 9200 block of Interstate 45 on the service road near Mount Houston Road, in Houston, Texas at 2:00 a.m. on May 22, 1994. She and her boyfriend got into an argument and Coibon got into a yellow station wagon driven by a man her boyfriend did not know. Coibon's boyfriend copied down its license plate number and called police after it drove away.

The car was owned by Jan Gruszka, who also goes by the first names Mieczslaw and Richard. He had been in prison for rape and murder in Poland, but fled the country while on a furlough in 1992 and moved to the United States. In spite of his background, however, it has not been established that Gruszka was driving the car himself when Coibon was last seen. He is being called a witness, not a suspect, as some investigators feel Coibon's boyfriend fabricated the story about the car and copied the license plate number from a vehicle in the parking lot of an Eastern European church nearby. Coibon's boyfriend is much older than she is and he allegedly abused her.

Eighteen months after Coibon vanished, the yellow station wagon she was reportedly last seen in was found at a wrecker storage lot. There was no blood or other signs of violence inside the car, but by then it had been purchased by someone else and cleaned, obliterating any evidence that might have been there. Coibon's case remains unsolved and foul play is suspected.