A 4-year-old boy almost ate a piece of candy dusted with highly poisonous strychnine and grocers were urged to pull the brand of candy from their shelves, investigators said Friday.

Investigators said they have not determined whether tampering or a problem in manufacturing was responsible for the presence of the substance, commonly used in rat poison, on a piece of "SunKist Fun Fruit Dinosaurs Candy" purchased in northern New Jersey.The product's distributor suggested that tests of the candy yielded a false positive for strychnine, saying that residues of a starch powder are common on the candy involved.

"There are probably more questions than answers at the moment," Bergen County Prosecutor Larry McClure said.