ROCKWELL CITY, Iowa (AP) — The initial field testing on hundreds of pills found inside a northern Iowa prison indicated they contained cocaine and the pain killer Demerol, but later testing came back negative for controlled substances, a Department of Public Safety spokesman said Monday.

The capsules discovered earlier this month at the North Central Correctional Facility in Rockwell City are now being examined at the state crime laboratory in Ankeny, which is expected to deliver the most accurate conclusion on what they contain, Sgt. Scott Bright said. He said the testing is being expedited, and results could be available within the next week or two.

State officials announced last week that 300 to 400 pills containing an “unknown” substance were discovered during routine searches at the minimum-security prison. A union representing correctional officers said the discovery was a “major security breach” that the Iowa Department of Corrections was trying to keep under wraps.

Bright confirmed Monday that prison staffers conducted a field test Sept. 8 that found white capsules tested positive for the presence of cocaine, and orange capsules tested positive for Demerol. But he said additional field testing last week by agents from the Division of Narcotics Enforcement and the Division of Criminal Investigation came back negative for any controlled substance.

Field tests are commonly used by police officers to try to identify illicit substances but considered far less accurate than testing done by trained scientists in the laboratory.

Department officials have not said how the pills got inside the prison.