A defense expert testified Friday that the St. Paul police crime lab's key drug testing instrument was not properly vented, possibly spewing drugs into the air and causing contamination.

The testimony came on the seventh day of a hearing that has far-reaching implications for criminal investigations even though it will only directly affect four cases. Sweeping changes have been implemented at the lab even though dense, contentious testimony has stretched across three months, with promises to extend into October. A judge's decision is not expected until late this year.

Former Minnesota Bureau of Criminal Apprehension (BCA) scientist Glenn Hardin's turn on the witness stand capped the most recent testimony in Dakota County District Court, which tested the patience of everyone involved.

Judge Kathryn Davis Messerich started Friday with a stern if exasperated directive to the defense and prosecution, who squabbled bitterly Thursday: "This has to end sometime."

Hardin testified that a tube that expels excess drugs should be connected to a fume hood. But according to testimony from lab staff and drawings they produced in court, the hoods are located in a different room from the testing instrument, Hardin testified.

"It's all suspect and unreliable and untrustworthy," Hardin said of suspected drug evidence that has entered the lab. He also said that the air in the lab was unsafe to breathe. Lab staff had testified that they had little or no knowledge of how the hoods were maintained, or if they ever were tested.

Public defenders Lauri Traub and Christine Funk have challenged the lab's work in a handful of Dakota County drug cases, which prompted the county attorney's office to throw out those results after three days of testimony in July revealed widespread problems. The State Patrol and law enforcement agencies in three metro counties also promptly stopped using the lab.

The debate now is whether the evidence in those cases was so poorly handled in St. Paul that the BCA should be prevented from retesting them because of possible contamination.

Hardin testified Friday that the lab's ventilation was unsafe and that maintenance records show that the "sensitive" testing instrument was not cared for properly by staff. Traub and Funk had previously presented testimony that the machine's tube was once clogged with a white substance, possibly drugs.

Dakota County Chief Deputy Attorney Phil Prokopowicz steered Hardin away from possible contamination in the testing room. At stake, Prokopowicz said, was whether the leftover evidence that the BCA could retest might be contaminated. It was kept in a separate room and then locked in a vault overnight.

Prokopowicz also went hard at Hardin's lack of direct experience in a drug chemistry lab. Hardin worked in toxicology at the BCA for 19 years and is familiar with the testing instrument, but testified that he had not worked with bulk suspected drugs.

Under cross-examination by Prokopowicz, Hardin also testified that it would be difficult for contaminants to penetrate sealed plastic bags. Staff had testified that evidence arrived and was kept in sealed plastic bags.

Under questioning by Traub, Hardin testified that if drugs spewed from the testing instrument, it could settle on surfaces and tools, contaminating the evidence as it's weighed, stored and moved around the lab.

Some criminalists previously testified that they didn't always change gloves between cleaning their workstations and handling samples, and sometimes used a tool more than once to collect samples from bulk evidence.

The hearing has prompted a review of past and pending drug cases in Dakota, Ramsey and Washington counties. The lab's director was replaced, and the city revealed Thursday that it's paying two consultants about $140,800 to review the lab's drug chemistry, fingerprint and crime scene units.

Police Chief Thomas Smith and Mayor Chris Coleman have said they would like to investigate possible accreditation, although the city has not made a firm commitment to it.

Testimony in the case started in July. It resumed in August and then again Thursday and Friday. It's also scheduled for Oct. 23, and possibly Oct. 24.

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