ROCKWELL CITY, Iowa (AP) — Lab results show hundreds of capsules found at a northern Iowa prison tested negative for any controlled substances. The state Department of Public Safety made the announcement Monday about the 300 to 400 capsules found earlier this month at the North Central Correctional Facility in Rockwell City. The Iowa Division of Criminal Investigation Criminalistics Laboratory completed an analysis of the capsules.

The pills contained an unknown substance, prompting a state drug investigation. Initial field testing indicated they contained cocaine and the pain killer Demerol, but later testing came back negative for controlled substances. State officials have not said how the capsules got inside the prison.