Police raided an Oxford house on the trail of a batch of high-strength heroin which caused 12 users to overdose.
After obtaining a warrant, officers searched the property in Salter Close, Grandpont, at about 7.30am on Wednesday, February 11.
No heroin was found. One person was arrested for possession of cannabis but later released without charge.
Oxford police spokesman Lucy Ferguson said: "We are determined to find who is responsible for supplying this drug and where it came from, and appeal for any information the public can give us."
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