San Francisco Police Chief George Gascon said his department went public on this issue on Tuesday night as a matter of integrity, but this is a damaging case. Already, the department has shut down all drug testing in its crime lab, some past convictions may not stand up, and future cases may be in jeopardy.
"We do not know the scope of the problems, dealing with this employee, but we'll get to it," said Gascon.
Gascon described an investigation that will cost his department's crime lab time, money, credibility and possibly, some convictions.
"We are very certain that this is all localized to a single individual. At this point, we have absolutely no evidence for believing that it involved anybody else," said Gascon.
That one person is Deborah Madden, a civilian employee who spent 27 years with the department before retiring March 1, 2010.
She was working in the crime lab when ABC7 took pictures of her and the lab in 1994.
Last December, investigators noted small amounts of cocaine missing from evidence.
They suspect Madden of stealing the drug for her personal use, beginning last fall, but have yet to arrest her on those charges.
"One of her supervisors noticed in late December that some of the packaging and some of the material appeared to be tampered with," said Gascon.
"In any drug trial, the chemist who tests the drugs is a witness and is an essential witness. And the fact that all these improprieties have taken place, if true, goes to the credibility of that witness and goes to the prosecutability of every case that he or she is involved in," said ABC7 legal analyst Dean Johnson.
If Madden did testify in such cases, she could also face charges of perjury. Police and the district attorney would not estimate how many cases they might have to question or re-rest, but potentially, it is a high number. The crime lab looks at as many as 50 narcotics cases every day.
"As necessary, we will retest the narcotics that are currently involved as evidence in cases that are pending, and re-file those cases if necessary," said San Francisco District Attorney Kamala Harris.
Madden declined to be interviewed when ABC7 called her Tuesday night. San Francisco police say she had been on a leave of absence since December, due to health issues.
On March 3, the San Mateo County Sheriff arrested her on an unrelated gun charge. They had searched her home last month. Along with the gun, they also found a small amount of cocaine.