During the early part of the 20th Century there was a massive oil strike in Cromwell, Oklahoma. This bought in people to work the oil fields and Gamblers to fleece them out of their money.

Sometimes, for the good of the system, some poor soul would get wacked in order to provide a sort of lesson to the other Bums out there that might think of not paying off their losing bets. The bodies were normally disposed of in a Crude oil tank by just dropping them through the hatch found on top of each tank.

The bodies, being lighter than oil, would sink to the bottom and not be found until the tank was drained for a work-over/service which was normally every 20 years. (Tanks at a tank farm are never drained entirely during routine use. There is always a few feet of oil in the bottom that the roof floats on. The floating roofs weigh 202,000 pounds, so if they hit the bottom they can crack the floor.)

By the time the bodies were being found the oil boom was long since over and all the Gamblers had moved on.

Perhaps who ever dumped the body was just trying to be old school about it.