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. He was staying with his parents in the 3900 block of Gull Court. At 2:00 p.m. on the day of his disappearance, Mansfield 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 former roommate. Smrekar had also a student at Lincoln College; he majored in English communications. He had been dismissed from the school months earlier, however, due to poor grades. 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 (worth $4) 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. 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 was also believed to be responsible for Mansfield and Martin's disappearances, but he was never charged in connection with them.

A photograph of Smrekar is posted below this case summary. In October 2011, shortly before he died in prison, he confessed to Mansfield and Martin's murders. No information has been provided about the location of Mansfield's body, but, investigators announced that, in light of Smrekar's confession, they were closing Martin and Mansfield's cases.

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. Three of Mansfield's siblings live in the Chicago area and his parents live in Florida. His body has never been found.

Above: Smrekar, circa 2006