Somewhere in a plastics factory, a woman coughed, setting off a chain of events that has led to questions about DNA evidence in three local crime cases.
Evidence analysts at the Tucson Police Department's crime lab were working to match evidence samples to DNA from suspects about two months ago when they found the unknown woman's DNA in three unrelated cases: a rape, a murder and an assault, said Robert Blackett, police DNA testing supervisor.
The DNA profile for the woman didn't match any suspect, victim, crime-lab worker or crime-scene worker. And the same profile turned up in two more crime labs in Florida.
While they can't be certain, officials deduced the disposable plastic test tubes they used in their analyses were contaminated at the factory before they were shipped to the separate crime labs.
The first of the evidence in the three local cases now is being presented — and questioned — in court. While those involved say the DNA problem will complicate the cases, they say it's not expected to pose major obstacles.
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The problem isn't as bad as a contamination in which one suspect's DNA is transferred to other cases, but it does show contamination is a real possibility, said Howard Wine, who is representing a defendant in one of the three local cases.
"DNA results are not infallible," he said.
First tainted test in court
The first of the tainted tests came up in court on Friday in the case of Danny Lopez, a Tucson man suspected of attacking seven women between May 2004 and February 2005.
Tests showed Lopez's DNA matched DNA found in four of the cases and his finger and palm prints matched those left at two scenes.
But when an analyst looked at a pair of hoop earrings seized from Lopez's house and belonging to the victim of an assault that happened on Feb. 24, the scientist found the unknown woman's DNA.
Prosecutors filed a motion with Pima County Superior Court Judge Kenneth Lee asking that jurors be kept in the dark about the unknown DNA.
Deputy County Attorney Shawn Jensvold wrote it is "irrelevant to any issue or evidence to be introduced" in the case.
He wrote that the trial "hangs significantly (although certainly not entirely) on the validity of the DNA evidence," and the problem "has the potential to mislead the jury to believe that none of the DNA results can be trusted."
The motion was denied and the earrings came up in DNA testimony on Friday and will be mentioned again during closing arguments this week, said Wine, one of Lopez's attorneys.
"We're leaving it to the jury to decide if the actual contamination shakes whatever faith they would have otherwise developed in the DNA results presented," Wine said.
Test tube contamination
After the analyst found the unknown DNA on the earrings, the same profile came up again on a handgun seized by police during an August 2004 aggravated assault investigation, according to the prosecutors' motion to exclude in the Lopez case.
Then the woman's profile matched DNA on a cigarette butt linked to a homicide investigation.
When analysts contacted the Florida Department of Law Enforcement's crime laboratory, which maintains a national database of unknown DNA profiles, they learned the same unknown woman's DNA had been detected in the two Florida labs.
In the Florida cases, the unknown woman's DNA came up in blanks, which are supposed to have no DNA and are used as a quality-control assurance, said Suzanne Livingston, forensic services director for the Florida Department of Law Enforcement, which analyzes close to 8,000 cases a year.
The crime labs probably each received a shipment of contaminated test tubes from the same supplier, although they are unsure which one, said Susan Shankles, the Tucson Police Department's crime lab superintendent. The local DNA unit handles around 500 cases a year.
The Florida agency blamed the problem on Applied Biosystems Inc., a California-based supplier of plastic test tubes, according to a report in the Orlando Sentinel. That newspaper reported that the company agreed the contamination happened at its factory and had found a solution to the problem. A company manager did not return a call to the Arizona Daily Star on Monday and Tucson police officials have not yet disclosed their test tube suppliers.
Both Blackett and Shankles said the most likely scenario involved a factory worker who was not wearing a mask and either coughed or sneezed on a set of tubes.
"The main thing for people to understand is, this was discovered because of vigorous quality-control standards," Livingston said. "It isn't an error. It's an unforeseen circumstance and we're doing what we should."
A frustrating problem like this turns up every few years, Blackett said. But, typically, an unknown DNA profile is linked to a lab analyst or crime-scene worker, Shankles said.
For now, Tucson analysts have stopped using a set of possibly contaminated supplies and have alerted other DNA analysts around the country, Blackett said. Starting next week, the local lab will sterilize any equipment that can't be certified as DNA-free using ultraviolet light, Shankles said.
