Police say Rockland Mann, 51, took the drugs from surgery patients then then altered what was left to disguise the missing medication.

Kettering Police Spokesman Bill Torok said, " He might have been diluting it or making it look like the proper amount was in the dispenser."

A grand jury indicted Mann on charges of theft of drugs and tampering with drugs.

As a result of a plea agreement reached Thursday, Mann pleaded guilty to the tampering charge, and the state dropped the charge of theft.

Investigators said the drug thefts had been going on for months. Hospital staffers caught onto it, realizing their patient's pain killers weren't working very well.

A spokesman for the hospital would not comment beyond saying that Mann is no longer a nurse at Kettering Memorial.

Mann's attorney, Brent Rambo, said his client is remorseful and has cooperated with police from the beginning of the investigation.

Rambo said Mann no longer has a license to work as a nurse.

Mann will be sentenced in August. He faces up to five years in prison and a maximum $10,000 fine.