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San Francisco District Attorney George Gascón, pictured when he was the city's police chief

Criminal charges will not be filed against the former San Francisco Police Department crime lab employee whose alleged pilfering of drug evidence last year prompted the closure of the drug lab and the dismissal of hundreds of prosecutions, authorities said Friday.

Debbie Madden, 60, of San Mateo, a former civilian criminalist at the lab, admitted to taking small amounts of cocaine spilled from evidence on five occasions between October and December 2009.

Police Chief George Gascon ordered the drug lab closed in March.

Amid the scandal and other questions raised about the integrity of testing at the lab, prosecutors with the San Francisco District Attorney's Office dismissed hundreds of new and ongoing drug cases.

A brief statement from the state attorney general's office today said that after an "exhaustive evaluation" it had determined that it would not pursue charges against Madden.

San Francisco District Attorney Kamala Harris asked the attorney general's office in April to take up the case because members of her office would be called to testify in any prosecution.

"I'm incredibly disappointed," Gascon said today of the attorney general's decision. "I believe that we had a good case."

He acknowledged that the primary evidence was simply Madden's admissions to investigators, and that there was limited physical evidence of the thefts.

Jim Finefrock, spokesman for the attorney general's office, said today that his office made the decision Dec. 2.

"There just wasn't sufficient evidence to prosecute her," Finefrock said.

He noted that Madden is still facing an unrelated felony cocaine possession charge in San Mateo County, and the charges his office were considering would likely have constituted misdemeanor theft.

The investigation into Madden's activities at the crime lab is now almost certainly concluded.

"We're going to evaluate, but more than likely it will be over," Gascon said.

Paul De Meester, Madden's attorney, said he learned of the attorney general's decision Thursday.

"She and I are very happy about this," De Meester said. "It lifts quite a burden from her."

Madden's felony charge in San Mateo County is for unrelated alleged evidence found at her San Mateo home during a search by police.

San Mateo County Chief Deputy District Attorney Steve Wagstaffe said today that case is due back in court Jan. 18. Though the case has not resolved yet, he said Madden would be eligible to be sentenced to a court-ordered drug treatment program.

Wagstaffe said his office would only have been able to charge Madden in connection with the crime lab had she brought drugs from the lab back to her home, and said there simply was no evidence of that.

"We did not see this as an appropriate case for San Mateo County," he said.

Madden went on leave from the police department in December 2009 and retired in March.

In addition to the alleged drug thefts at the lab, San Francisco prosecutors had also complained Madden was failing to show up to court to testify in cases in which she had tested the evidence.

It was later revealed that police never told prosecutors of Madden's prior conviction for domestic violence in 2008, information that prosecutors are required to turn over to defense attorneys in order for them to challenge her testimony in court.

Police and the district attorney's office have since developed new protocols for such evidence to be disclosed.

A state audit in March of the lab's drug unit also found significant problems, principally that the unit was overworked and understaffed and "sacrificing quality for quantity."

Other problems were found with storage and upkeep of the lab, and training procedures.

Gascon has said he wasn't informed of the allegations against Madden until late February. He ordered the drug lab closed in early March.

De Meester alleged today that his client "has been scapegoated as the cause of the problems of the lab."

"This crime lab has systemic, long-term problems that are the responsibility of the city and county of San Francisco and the San Francisco Police Department," De Meester said.

"And this has nothing to do with Debbie Madden," he said. "Debbie Madden was the victim of the mismanagement of the lab."

De Meester said the "enormous workload" that the department imposed on the lab staff was "a prescription for disaster."

Gascon noted today that the crime lab has since been reaccredited by a national crime lab accreditation agency, and that its DNA, firearms and fingerprint testing units continue to run and are working to eliminate backlogs in evidence testing.

Gascon said that the drug unit continues to send evidence to outside labs for testing, while officers on the street are using presumptive testing kits in order for prosecutors to re-book arrestees while awaiting lab results.

With the city's current budget constraints, Gascon said that procedure represented "a good business model," especially considering the costs of the Madden investigation and the subsequent fallout.

"The upside of all of this is while this is very painful, it's highlighted some problems in the lab … and we have taken a very in-depth look at the operation," Gascon said.

"We have made substantial changes … to reduce the likelihood of anything like this ever happening again," he said.