By far the most famous case was the murder of eight-year-old Timothy Mark O'Bryan at the hands of his father, Ronald Clark O'Bryan, in Houston, Texas. The child died at 10 p.m. on 31 October 1974, as a result of eating cyanide-laced Pixie Stix acquired while trick-or-treating.
To make it appear more like the work of a random madman, O'Bryan also gave poisoned Pixie Stix to his daughter and three other children. By a kind stroke of fate, none of the other children ate the candy.
The prosecution proved the father had purchased cyanide and had (along with a neighbor) accompanied the group of children on their door-to-door mission. None of the places visited that night were giving out Pixie Stix. Young Mark's life was insured for a large sum of money, and collecting on this policy has always been pointed to as the motive behind this murder.
Though the case was circumstantial (no one saw the father poison the candy or slip the Pixie Stix into the boy's bag), Ronald O'Bryan was convicted of the murder in May 1975. He received the death sentence and was executed by lethal injection on 31 March 1984 (not on the poetically-just 31 October as is often recounted in off-the-cuff retellings of the case).
The O'Bryan murder was an attempt to use a well-known urban legend to cover up the premeditated murder of one particular child. (Note that for this explanation of the boy's murder to have been believed, the legend had to have been in widely circulation by 1974.) Though cold-blooded and horrible to contemplate, this crime still does not qualify as a genuine Halloween poisoning because there was nothing random about Timothy O'Bryan's death.
(The spectre of the mad poisoner from the 1982 Tylenol murders was similarly employed by various murderers attempting to cover their tracks.)
What could the terrorists do to us that would be more horrific than what they did on September 11? How about attacking millions of innocent children? And I wouldn't be so naive as to think that because you know your neighbors you are less vulnerable. These people aren't going to hand it out. They will get it into retail outlets. (Who runs a large number of this nations convenience stores?) Anybody remember the Tylenol scares that prompted the extra protection sealing of over the counter medicine bottles? We really don't know how far the reach of these monsters extends. Why take that chance? Take the kids to a fair or something else fun instead, and don't apologize for putting their safety first.