San Francisco's public defender, Jeff Adachi showed reporters an enlarged copy of a drug report signed by technician, Debbie Madden and a second copy of the evidence retested by this lab in San Mateo County.
Jim Norris is now a forensic consultant who was in charge of the San Francisco lab from 1995 to 2004. Using grated cheese to demonstrate his point, Norris showed ABC7 what Madden claimed the sample was supposed to weigh -- and what the lab ended up with.
"Obviously some sample is used up in the analysis so you always expect the weight to go down by a small amount, but the amount used is in the milligram range, so you wouldn't expect much of the change in the weight," he said.
Adachi says in a criminal case, weight matters.
"It can often make the difference between a person going to prison or county jail or the case being ultimately being dismissed," he said.
Madden is being investigated for supposedly stealing and using some drug evidence -- about 250 cases have been thrown out.
The lab remains closed and Adachi is now calling for an independent crime lab with no police involvement.
"If it were a private lab, the private lab would come to San Francisco, would set itself up at no cost to the city. We would simply have to enter into a contract where evidence was tested," he said.
The police department would not comment on the proposal.
"It's something that we hope will be resolved soon but we are not rushing anybody. We want the job done correctly the first time and we want to know about everything that needs to be corrected," Lt. Lyn Tomioka from the San Francisco Police Department said.
Mark Hawthorne is a former San Francisco crime scene investigator who now teaches at City College.
"By having a private lab, it alleviates allegations of bias," he said.
Still he says, there is no substitute for a government-run crime lab.
"As a matter of fact, many times the hiring qualifications are not as stringent as are in governmental agencies," Norris said.
No word on when the lab will re-open.