Steve, suddenly we have Jeremy now in a cocaine induced state....how did he manage to turn up at the farm a very short time later in a calm and normal state, no sign of a 'cocaine induced state', shakes from adrenaline....nothing. A person on cocaine is not in control steve.
A Cocaine 'high' lasts from between 30mins to 2 hours, not very long if within that time Jeremy had to get to and from WHF. With no idea how long his high would last it's all a bit unpredictable. Also it's taken for a good time, it makes people very talkative and happy. You tend to love everyone when on a high. The low afterward can be so bad it can cause suicidal thoughts.
I don't believe anyone would take cocaine on it's own to help them kill.
Maybe cocaine mixed with other drugs, possibly not even available back in 1985 and certainly the effects of these drugs could never have worn off in such a short time.imo