Snopes.com classifies the panic as "false". It is considered to have been blown out of proportion by the news media. To date there have been several studies by independent and law enforcement agencies to determine the veracity of these claims, none of which have provided any verifiable evidence a child has ever died or been seriously harmed by candy picked up while trick-or-treating. Though needles have turned up on an extremely rare basis, this may have been the result of a copycat effect based on the news reports.
The first event took place in 1964, where an annoyed New York housewife started giving out packages of inedible objects to children whom she believed were too old to be trick-or-treating. The packages contained items such as steel wool, dog biscuits, and ant buttons (which were clearly labeled with the word ”poison”). Though nobody was injured, she was prosecuted and pleaded guilty to endangering children.
The second milestone in the spread of the candy tampering myths was an article published in the New York Times in 1970. This article claimed that "Those Halloween goodies that children collect this weekend on their rounds of ‘trick or treating’ may bring them more horror than happiness." (28 Oct 1970, p. 56). The article then went on to give specific examples of potential tamperings.
Upon closer examination nearly all of these claims were false or hoaxes created by the child. Within the reports of candy tampering Best has only found five child deaths that were initially thought to be caused by homicidal strangers.
In 1970, a 5-year-old boy died after eating his uncle's hidden heroin stash. The family tried to protect the uncle by creating a story about drugs being found in the child's Halloween candy.
In a 1974 case, an 8-year-old Pasadena, Texas boy died after eating a cyanide-laced package of Pixy Stix. A subsequent police investigation eventually determined that the poisoned candy had been planted in his trick-or-treat pile by the boy's father, who also gave out poisoned candy to other children in an attempt to cover up the murder. The murderer, who had wanted to claim $20,000 in life insurance money, was executed in 1984.
By 1985, the media had driven the hysteria about candy poisonings to such a point that an ABC News/Washington Post poll that found 60% of parents feared that their children would be injured or killed because of Halloween candy sabotage.
This collective fear also served as the impetus for the "safe" trick-or-treating offered by many local malls.