A Dakota County district judge allowed a hearing about the quality of St. Paul police crime lab testing to continue Wednesday, despite what she described as a "sea change" in the focus of the proceedings.

The court began hearing testimony in July about shoddy efforts in the county's drug cases. But the hearing has taken a different direction as it begins to examine whether the work was so questionable it should preclude the Minnesota Bureau of Criminal Apprehension from retesting evidence first handled by St. Paul police.

"I believe the defense has raised a significant issue" about possible contamination of the evidence, Judge Kathryn Davis Messerich said, adding that there was enough doubt to continue with testimony.

Public defenders Lauri Traub and Christine Funk are challenging the lab's work in seven cases, consolidated into one hearing that will continue Friday and on two days in September. Only one case has been retested by the BCA.

Dakota County Chief Deputy Attorney Phil Prokopowicz had requested that the judge cancel future hearings because of the change in focus, noting that his office was no longer using St. Paul's test results. He argued that the narrower focus -- the defense's concerns that possible contamination could taint retesting at the BCA -- should be addressed in individual hearings.

Davis Messerich said addressing the issue case by case would be "extraordinarily inefficient," and Funk argued that the public defender's office does not have the money to hire expert witnesses for seven hearings.

Prokopowicz said Wednesday that Davis Messerich had helped narrow the hearing's scope. "We're pleased," he said of the judge's guidance.

In Wednesday's testimony, criminalist Roberta DeCrans said that in one instance when she ran a cleaning solvent through a machine, results mimicking a substance showed up on a graph. She testified that she interpreted it as a "column bleed," which occurs when a tube coated with a polymer inside the machine leaks some of the polymer into a part of the machine that tests for possible drugs.

"Could it be contamination?" Traub asked.

"It could be column bleed," DeCrans said.

"My question was, 'Could it be contamination?'" Traub asked.

"I guess it could be," DeCrans said.

Traub picked DeCrans apart for not testing further to verify that her results indicated column bleed.

Wednesday's testimony didn't stray far from information that came out in July, when widespread problems were identified.

The department quickly suspended all drug testing, the lab director was replaced, and three counties and the State Patrol, which relied on St. Paul for drug testing, took their materials to the BCA for examination.

The judge is expected to issue her decision in the case later this year.

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