
Paraquat murders

The paraquat murders were a series of indiscriminate poisonings carried out in Japan in 1985. Police were unable to gather any evidence about the murders other than they were caused by a poisoned beverage that was left inside or around vending machines. All the beverages were poisoned with the herbicide paraquat except for one which was poisoned with diquat.
Events.
The first poisoning and death occurred on April 30, 1985 in Fukuyama, Hiroshima. This drink was found on top of the vending machine. After this, eleven more murders occurred between September 11 and November 17. Most of these drinks were retrieved from outside the vending machine. Vending machine operators posted warnings on machines telling people not to consume drinks found in or around the machines, after which the poisonings stopped. 
The culprit was never found.
It was established that at least one other unknown person attempted to imitate the paraquat murders by putting lime sulfur into drinks in Tokyo. There were also a small number of people who attempted to poison themselves in a method imitating the murders.