The Murder of Gary Simmons

In the heat of the 1970's oil crisis, many gas station owners did what they had to, in order to survive. "Allegedly" Gary Simmons was one of those people. Gary was set to testify in federal court against some key players in the black-market fuel ring. Shortly before the court case is set to take place, Gary goes to purchase a horse and is never seen again. Was this a case of greed, or was this something much deeper with big players in the mix?