U.S. District Judge Susan Illston in San Francisco declared a mistrial after jurors in the trial of Deborah Madden, 62, of San Mateo, told her they had reached an impasse.
Madden was charged with violating a federal law that makes it a crime to obtain a controlled drug by means of fraud, deception or subterfuge.
Her defense lawyers argued that there was no proof that she used deception or fraud to steal bits of cocaine evidence, as opposed to simply taking what was in front of her on her desk.
Madden's first trial on the federal charge also ended in a mistrial in October, when jurors were unable to agree on whether the element of deception or fraud had been proved.
Illston ordered prosecution and defense lawyers to return to court on Feb. 15 for a status conference to discuss the next steps in the case.
Madden admitted in a police interview in 2010 that she took some cocaine, but maintained she merely picked up trace amounts spilled during weighing.
Madden's actions and other problems at the laboratory led to the temporary closure of the facility's drug analysis unit and the district attorney's dismissal of hundreds of criminal cases that depended on evidence analyzed at the unit.
Prosecutors argued that Madden acted deceptively by working late more than usual in November and December 2009 so that she could take cocaine when no one was watching, and by opening a colleague's locked evidence locker and re-stapling an envelope that contained drugs.
Prosecution witnesses testified that 10 evidence envelopes analyzed by Madden and her two colleagues at the unit in late 2009 appeared to be missing a total of about one-half ounce of cocaine when they were reweighed during the investigation.
The mistral came after three days of testimony last week and about 16 hours of jury deliberations spread over four days this week.