Dakota County prosecutor Phil Prokopowicz is trying to stop a hearing that could reveal more problems with the St. Paul police crime lab, which has undergone major overhauls since July.

Prokopowicz, the chief deputy county attorney, wrote a letter to Dakota County District Judge Kathryn Davis Messerich on Tuesday arguing that allowing the pretrial evidentiary hearing to continue "is to allow defense counsel to engage in nothing more than a 'fishing expedition.'"

Public defenders Lauri Traub and Christine Funk challenged the lab's work in a July hearing that will continue Wednesday, Friday and in September.

The July hearing revealed widespread problems, including no oversight of evidence handling, no documentation of testing procedures and no peer review of test results.

This week Traub and Funk plan to call expert Glenn Hardin, who would testify that retesting evidence taken from the lab is not scientifically sound. As a result of testimony, St. Paul suspended its drug testing and the Minnesota Bureau of Criminal Apprehension (BCA) was directed to retest many of its pending cases.

"Mr. Hardin's position is that there are too many unknowns with the [lab's] analytical procedures, and because of this, any analysis that is performed after the evidence has passed through the [lab] (e.g. sending the sample to another forensic laboratory such as the BCA for subsequent testing) cannot rectify what has already possibly occurred in the [lab]," Traub wrote to the judge last week.

Prokopowicz said in his letter that chain-of-custody and potential contamination problems should be addressed at trial on a case-by-case basis to avoid significant costs, time and duplication.

"Defense counsel has failed to identify any general policy, protocol, or practice by the Crime Lab that would lead to inherent or widespread contamination that would impact retesting performed by the BCA," he wrote.

The defense's stance is that the lab's poor recordkeeping and a lack of oversight of evidence handling and equipment and workplace sterilization raise substantial doubt.

"It is simply unknown what is and what is not contaminated," Traub wrote.

Prokopowicz's request will be addressed Wednesday.

Lab staff previously testified that some of their practices were not scientifically sound. Staff also said they were not aware of basic documentation required in handling and testing possible drugs. As a result, the lab's director was replaced and three county attorneys started reviewing past and pending cases. The Police Department announced this week it is hiring outside experts to review the lab's practices.

Traub and Funk are attempting to raise enough doubt about the lab's work to throw out evidence in eight drug cases. Davis Messerich will likely issue her decision late this year.

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