A St. Paul police crime lab analyst testified Friday that she could not recall asking anyone to evaluate a testing instrument even though she thought it was interfering with test results.

Public defender Lauri Traub noted that according to maintenance logs, the machine in question wasn't serviced until several months after those tests had been conducted.

Traub and public defender Christine Funk are trying to raise enough doubt about the lab's evidence handling to stop the Minnesota Bureau of Criminal Apprehension (BCA) from retesting the same evidence. They believe that evidence could be so contaminated that no tests would be valid.

Criminalist Roberta DeCrans said that she conducted tests in May 2011 that experienced interference she attributed to "column bleed," which is when a polymer in the machine leaks and appears on a graph mimicking a substance.

The machine was serviced in January 2011, and wasn't serviced again until January 2012, Traub said. She asked DeCrans if the apparently faulty part, a tube that is coated with the polymer, should've been replaced.

"I guess that would be a possibility," DeCrans said.

"Why didn't you call maintenance when you saw that significant column bleed?" Traub asked.

DeCrans said she could not recall why she didn't act.

Traub trained her questions on the lab's lack of written "standard operating procedures," and the absence of safety nets to vet results.

Under questioning by Dakota County Chief Deputy Attorney Phil Prokopowicz, DeCrans testified that she tested evidence numerically as it was labeled. Under cross-examination by Traub, she said that she prepared the evidence in numerical order, but didn't always test them in that order.

The minor detail and vocabulary spat are part of the defense's attempt to paint a picture of the lab as a do-as-you-like workplace where definitions and procedures varied from one criminalist to the next.

To counter the defense's doubts, Prokopowicz walked DeCrans through her handling of suspected drugs. She said that evidence is delivered in sealed bags, and that once a sample is removed for testing, the remaining evidence is sealed in a new bag that is then sealed in the original bag.

DeCrans testified that she never saw any bags that appeared to be tampered with.

In questioning aimed at dismantling the defense's attack on the cleanliness of testing instruments, Prokopowicz asked DeCrans about a machine showing one sample tested negative for drugs while a different sample tested positive in back-to-back tests.

Traub and Funk are challenging the lab's work in seven Dakota County cases in one consolidated hearing that began in July and continued this week. Two days of testimony also are scheduled for September, and a third is likely.

Prokopowicz asked District Court Judge Kathryn D. Messerich on Friday to remove three cases from the hearing because evidence in one case was never tested by St. Paul, and because in two cases there was insufficient evidence leftover for the BCA to retest.

He asked the judge to remove part of a fourth defendant's case because of insufficient evidence. Prokopowicz said the cases will be removed, although a formal order was not issued Friday.

The county attorney's office has said it is no longer using St. Paul's test results in Traub's and Funk's cases. Prokopowicz said that the BCA is retesting the evidence, which should be completed by late next week.

One retested case has been shown to contain drugs, supporting St. Paul's initial results.

Messerich is expected to issue her decision on the case later this year.

Chao Xiong • 612-270-4708 Twitter: @ChaoStrib