A prosecution witness Tuesday defended practices similar to those used at the embattled St. Paul police crime lab, concluding testimony in four cases that challenged the accuracy of the lab's drug tests.

Dakota County Judge Kathryn Davis Messerich's decision, expected early next year, could have a wider impact than in the cases in question. Testimony earlier this year already prompted the St. Paul police chief to stop narcotics testing at his lab, exposed lax oversight of labs in Minnesota and forced a reassessment of numerous criminal cases, including one dismissed because of contradictory results.

Defense attorneys have attacked workplace practices at the St. Paul crime lab over several days of testimony in July, August and September, raising doubt about the purity of suspected drug samples that sat unattended on work benches while criminalists were in another room. But Tuesday, a criminalist for the state Bureau of Criminal Apprehension called by the prosecution testified that many of his practices were similar to those in St. Paul.

Eric Grunwald, a criminalist in the BCA's drug chemistry unit, testified that he left suspected drugs unattended on his desk while in another room testing samples. He also testified that although the BCA has written standard operating procedures for many things, he could use his own discretion about when, how and how often he cleaned his desk and tools. The defense had trained a critical eye on similar practices by staff at the St. Paul crime lab in an attempt to raise doubt about possible contamination of evidence.

Another witness, John Kroska, testified that he serviced two of the lab's key testing instruments the past four years. The defense had focused on how the instruments were not vented outdoors, and lacked fume hoods to vent out noxious fumes.

Kroska testified that he found white residue on a tube that expels waste from the instruments, and that although they were not vented outdoors, they were vented into a chemical filter, a proper alternative.

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At a news conference in July, St. Paul Police Chief Thomas Smith said he was not aware of major issues with the department’s crime lab until then.

Public defenders Lauri Traub and Christine Funk are challenging the police crime lab's credibility in the four cases, trying to raise enough doubt about contamination to render any BCA retesting of the samples inadmissible in court.

Previous testimony revealed that lab staff had varying testing and cleaning practices, there was no oversight for questionable results and there was little documentation for testing procedures compared to accredited labs such as the BCA lab.

The BCA retested evidence in the cases, and the results supported St. Paul's results showing the presence of narcotics, said Phil Prokopowicz, Dakota County chief deputy attorney.

Police Chief Thomas Smith stopped the lab's drug testing soon after testimony began, and the city has hired two consultants to review and revamp the lab's drug chemistry, latent print and crime scene units.

The lab continues to collect evidence but has stopped analysis of all evidence, police spokesman Howie Padilla said.

The BCA began retesting about 175 cases that were initially tested by St. Paul, and it is now taking on all cases from Dakota, Ramsey and Washington counties that would previously have been processed in St. Paul.

The Ramsey County attorney's office dismissed a drug case against Pahoua Yang in September when tests by the BCA showed no controlled substances. St. Paul initially tested the evidence positive for methamphetamine.

Yang's attorney recently filed a motion to suppress evidence from the St. Paul and BCA labs in an unrelated drug case against her.

Last week, the BCA notified the Dakota County attorney's office that a pill it tested was positive for a controlled substance. St. Paul initially tested it negative for narcotics, Prokopowicz said.

With testimony complete, the prosecution and defense will submit written briefs arguing their case in November and December. Messerich will have up to 90 days to issue her decision.

Funk said, if anything, she hopes the hearing will encourage attorneys to dive into forensic science and investigate test results on their clients' behalf.

"That means going down and talking to the scientist and educating yourself on the science," Funk said.

The defense already won one victory in August, when prosecutors decided not to submit St. Paul's test results in the four cases, which was the initial focus of the hearing and original argument Messerich was to take under advisement.

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