READING, Pa. (AP) — A district attorney in southeastern Pennsylvania issued a public health warning Monday in the wake of a series of drug overdoses, some of them deadly, believed to involve the same substance. Berks County District Attorney John T. Adams said that a dozen people overdosed over the weekend in the city of Reading, West Reading borough, and Exeter and Rockland townships. Three died.

The overdoses involved a substance believed to be cocaine laced with fentanyl or another opioid, he said. The drugs were packaged in clear plastic packets or baggies.

Detectives are awaiting the results of toxicology testing.

“We, as law enforcement, are combating this epidemic that has plagued our community with every resource available to us,” Adams said in a statement, adding: “It is critical that the community remain vigilant and check on family and friends who may be using these dangerous drugs.”

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