Mansfield was last seen in Rolling Meadows, Illinois on December 31, 1975. He was a student at Lincoln College in Lincoln, Illinois at the time of his disappearance, and was home for the Christmas holidays. At 2:00 p.m. on the day of his disappearance, he got a phone call and left a short time later, saying he was going to visit a friend in Arlington Heights, Illinois. He never returned and has never been heard from again.

Mansfield disappeared six days before he was scheduled to testify against Russell Smrekar, his roommate. Smrekar was also a student at Lincoln College; he majored in English communications. He was accused of stealing a guitar and some records from a dormitory room and Mansfield was a key witness against him in that case. After Mansfield's disappearance, the burglary charge against Smrekar was dropped for lack of evidence. The following year, he was accused of stealing two steaks from a Kroger grocery store. A witness in that case, Ruth Martin, has disappeared as well.

Smrekar was subsequently convicted of murdering Jay and Robin Fry, and was sentenced to 200 to 600 years in prison. He is eligible for parole every three years, but has been denied every time. Jay was the store clerk who saw Smrekar try to steal the steaks and was going to testify against him at the trial. Robin, Jay's wife, was pregnant at the time of her death. Smrekar is also believed to be responsible for Mansfield and Martin's disappearances, but he has never been charged in connection with them. A photograph of Smrekar is posted below this case summary.

Mansfield is a 1974 graduate of Rolling Meadows High School. At the time of his disappearance, he frequented record stores at Woodfield Shopping Center and in Arlington Heights and Chicago, Illinois. He reportedly worked at the Lincoln College radio station and dreamed of a job as a radio station music director. His family held a memorial service for him in about 1998.

Authorities have stated that the investigation into Mansfield and Martin's disappearances has never been closed and police still hope to resolve their cases. Both disappearances remain unsolved.

Above: Smrekar, circa 2006