An informant who was developed and frequently used by Shepherd when he was sheriff, testified before the 1990 federal grand jury that Shepherd gave him marijuana seeds and instructed him to plant marijuana patches around the vast rural areas of Grant County. The informant was to mark on a map the locations of the marijuana patches and let Shepherd know when the plants were ready to harvest. Several Saturdays during the summer, Shepherd would take out an "eradication team" to pull the plants but would leave a portion for the informant to harvest. Shepherd became known for his incredible ability to find and destroy marijuana.

It is unknown what connection Shepherd had with the "train deaths" or the drug smuggling operation connected to the murders, but it is obvious he had an interest in perpetuating a cover-up. Shepherd attempted to interfere with at least three different investigations. In 1990, Shepherd paid a visit to U.S. Attorney Chuck Banks to persuade him Jean Duffey should be ignored. In 1993, Shepherd told Detective John Brown his career would be better off if he concentrated his efforts elsewhere. And in 1995, Shepherd paid an inappropriate visit to the FBI about their investigation of the case, but it is unknown exactly what was discussed. Very little has been exposed so far about Robert Shepherd, but as time goes on, that will change.