No one suspected Cullen was murdering patients at St. Luke's until a co-worker found vials of medication in a disposal bin. The drugs were not valuable outside the hospital and were not used by recreational drug users, so their theft was curious. An investigation showed that Cullen had taken the medication. He was offered a deal by the medical facility: resign and be given a neutral recommendation, or be fired. He resigned and was escorted from the building in June 2002. Seven of his co-workers at St. Luke's later alerted the Lehigh County district attorney about their suspicions that Cullen had used drugs to kill patients. Investigators never looked into Cullen's past, and the case was dropped nine months later due to lack of evidence.