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Crime, Law and Justice
MPR News Staff

Hennepin County Sheriff's Office crime lab pauses DNA testing due to contamination

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The Hennepin County Sheriff’s Office has put DNA testing at its crime lab on hold as it works to determine the source of “sporadic DNA contamination.”

The sheriff’s office said it appears the contamination may be linked to “an external product we use in the DNA testing process.” In a statement Monday, it said that of 50,000 samples it’s reviewed so far, 75 “were potentially impacted with the unknown source.”

“Because the contamination is due to an unknown DNA profile, no criminal charges or convictions could have resulted from this contamination,” the sheriff’s office said.

Documents from the sheriff’s office and the Hennepin County Attorney’s Office state that the crime lab learned about the contamination in mid-September when a full DNA profile showed up in a “reagent blank” — a control sample that shouldn’t have contained any DNA.

The DNA profile was from an unknown male, and matched a profile from a discharged cartridge casing that was tested in 2022. The profile didn’t match anyone in the lab’s employee database.

A review of data going back to 2016 turned up other, random instances of the same profile contaminating samples — but it wasn’t previously recognized as contamination, because it didn’t turn up in a reagent blank until recently.

A Monday memo from the Hennepin County Attorney’s Office to defense attorneys, summarizing updates provided by the sheriff’s office crime lab, stated that other forensic labs across the country have found the same profile in samples in their facilities.

“The Crime Lab believes the contamination comes from a consumable product such as a plastic tube or plate. They are working with their supplier to determine the cause,” senior assistant Hennepin County attorney Dan Allard wrote in the memo. “The Crime Lab plans to run tests next week to try and narrow down the source of the contamination. The lab plans to take steps to eliminate or minimize the risk of future contamination and this likely means making changes to the products/equipment they use.”

Allard wrote that the crime lab was determining next steps for the 75 potentially affected samples, including possible re-testing. He said the county attorney’s office had requested but did not yet have a list of all the potentially affected cases.

While the source of the contamination is investigated, the crime lab has paused DNA testing. As of late September, lab officials estimated that pause could last three to four weeks.