WAKE COUNTY, North Carolina (WTVD) -- A Wake County worker charged with putting something in a co-worker's drinks to try to hurt her has resigned.In court documents, investigators say 33-year old Adrien Crawford committed the crimes between May 9 and May 22.According to a 911 call released late Wednesday afternoon, the suspect put something in the female co-worker's drinks on at least four occasions at an office building the county rents at 110 Horizon Drive in north Raleigh.Police say the co-worker noticed something in her drink and reported it to a manager, who then reported it to security. It was the security officer who called 911.In the 911 call, the man tells the dispatcher that after the first incident was reported a camera was set near the co-worker's cubicle."You see a bottle in his hand when he goes into the cubicle area. You see him searching in her bag. You see him motioning like he's pouring something. And you see him when somebody walks past he starts hiding. And as soon as the person leaves you see him dart out of there."That call was made on May 17; that's when Raleigh police began investigating.It's clear from the call that security officers for Wake County had been investigating for a while."So we got an employee that last week reported that something has been put in her drink on three consecutive days. So we got involved. We took it, you actually could see the substance in the drink. We got the substance sent off and tested. We put a camera in and we've seen someone go into the desk area and do what was reported."Crawford was arrested yesterday and charged with giving the co-worker "adulterated or unbranded food" in order to seriously injure her.He posted a $50,000 bond overnight, got out of jail, and faced a judge Wednesday morning. He was banned from all county property.The 911 caller says preliminary tests didn't provide enough information and more testing needs to be done.It's not clear if more charges could follow depending on the test results.