A DNA sample that was accidentally mixed up with another sample at the San Francisco Police Department’s beleaguered crime lab in 2008 has spawned at least two investigations and renewed calls for an independently operated lab.

The investigation stems from an anonymous complaint dated July 30, 2009, in which a whistleblower claimed that a DNA sample in a rushed trial had been switched to cover up a mistake. All evidence of the switch was then allegedly covered by re-labeling the samples and erasing details of the record on the computer, according to the complaint.

In its response to the American Society of Crime Laboratory Directors, the Police Department initially said in August 2009 there were no “instances of corrective action for Ms. Tahnee Nelson,” the criminalist who made the mistake.

More than a year later, after lab worker Deborah Madden was accused of stealing cocaine from evidence samples, that accrediting body completed an investigation into the anonymous allegations. Lab workers interviewed about the “sample switch” confirmed that “the sample mix-up did occur,” according to the inspection report.

“The analyst immediately reported this incident to the supervisor. The supervisor authorized the analyst to correct the tube labels and the sample processing proceeded.”

That investigation, which concluded in September, prompted an internal probe that wrapped up Friday. While police Chief George Gascon has yet to comment on that investigation, spokeswoman Lt. Lyn Tomioka said that the probe concluded that there was no cover up.

“At most it was a training error on the part of a new employee,” Tomioka said Friday. “When she brought it to the supervisor’s attention, immediate corrective action was taken. An investigation was conducted based on the whistleblower complaint, and it remains an active investigation.”

But defense attorneys are calling foul, saying the Police Department knowingly concealed information about the lab switch. Public Defender Jeff Adachi said it is another example of why the crime lab should be independently operated.

“To me, that August, 2009, letter clearly shows that the lab knew about the sample switch, but misrepresented or denied that it even occurred to the reporting agency,” Adachi said. “It raises serious doubts about any DNA testing going on in the lab.”

The crime lab has since undergone a major purging of personnel. Last month, the crime lab’s director Cydne Holt, resigned.

bbegin@sfexaminer.com

Bay Area NewsCrimeCrime & CourtsLocalSan Francisco

If you find our journalism valuable and relevant, please consider joining our Examiner membership program.

Find out more at www.sfexaminer.com/join/