A 12-year-old Pennsylvania boy says he found a razor blade in a package of M&M's while trick-or-treating over the weekend, prompting investigations by local police and the candy's manufacturer.

Matthew Hernley said he found a one-inch blade in a fun-size package of M&M's on Sunday, during his town's sanctioned period of trick-or-treating in Scottdale, Pa.

"I don't know which house I got it from, because every other house I think I got a pack of M&M's," Hernley told KDKA-TV.

Scottdale Police said they were investigating, but as the boy indicated, it would be difficult to determine from which house the candy was received.

"The package did not appear to be tampered with and we think this is probably is a manufacturing issue," a Scottdale Police officer, who was not authorized to speak to media, told ABCNews.com.

"Food safety and product quality are of paramount importance to Mars. We were very disturbed to learn that a consumer had a product safety issue within our M&M'S Funsize packaging," a spokesman for Mars Chocolate North America told ABCNews.com in a statement.

"We will continue to investigate to better understand the nature of this incident and work with the local authorities, if needed," he said.

Tampering with Halloween candy became a problem in the late 1970s and early 1980s when police departments reported incidents of children finding blades, pins and pieces of glass in their candy.

Beginning in 1982, the National Confectioners Association maintained a Halloween Hotline in which law enforcement agencies could report incidents of tampering, and some hospitals X-rayed children's candy for foreign objects.

Last year the NCA shut the hotline because "there is very little occurrence of tampering," said spokeswoman Susan Smith. "Tampering is extremely rare, and we don't even track it anymore because police just aren't seeing it," she said.