Go find me some verified reports of this actually happening, besides the one I mentioned. Major news organizations have tried and failed.
I'm not questioning the unfounded hysteria over halloween candy being tampered with. I believe that's merely news media looking for ratings. I due question your statement that specifically cites Christians being the culprits that spread these stories hoping to quell trick-or-treating. It sounds like you're generalizing and slandering Christians to suit your need.
Never underestimate the power that the devout & dull have to just be a collosal bore. :-)