That employee has been arrested and charged with buying crack on a Philadelphia street corner.
"What we're doing now is doing an audit on everything that she touched narcotics-wise, making sure the count is accurate with the count that was submitted by the officers," Philadelphia Police Lt. Ray Evers said.
For the past two years, 45-year-old Melanie Postell worked at the Police Forensic Science Center.
She was a legal service clerk who took in drugs and other evidence, labeled it with a bar code and then put it in a drop box.
Last Friday night, the police say she was on a North Philadelphia street collecting drug evidence illegally, buying a packet of crack cocaine from a drug dealer.
Action News asked Postell, "What happened Friday night? Can you tell us?"
She replied, "I can't tell you."
The police are now worried that if Postell had been buying drugs on the street, she might also have been tempted to tamper with evidence on the job.
"If there was 10 packets of heroin, [we're] making sure if she was the person involved in dropping that drugs that there were 10 packets of heroin," Evers said.
The police say drug evidence is heat sealed in plastic bags and then placed in a drop box that only the supervisor has access to.
They say it's very difficult for a civilian clerk like Postell to skim off a little for personal use.
But they can't take any chances, so they have to go back and examine two years worth of evidence she handled.
Postell says she never tampered with police evidence.
Action News asked Postell, "You can say categorically that you never took anything from the evidence lockers?"
She replied, "Yes."
Action News asked, "Didn't tamper with anything?"
She replied, "No, sir."
Action News asked, "So, you just had a problem Friday night and that was the extent of it?"
She replied, "Yes, sir."
Police also arrested Postell's husband James who was with her at the time of the alleged drug buy.
The police department is now reexamining its policy that exempts civilian employees from periodic drug testing.