Minnesota may be forced to drop thousands of driving-while-impaired cases and change the way it prosecutes others in the wake of a state Supreme Court ruling Thursday, prosecutors and defense attorneys agreed.

The state’s highest court ruled that defendants in drunken-driving cases have the right to make prosecutors turn over the computer “source code” that runs the Intoxilyzer breath-testing device to determine whether the device’s results are reliable.

But there’s a problem: Prosecutors can’t turn over the code because they don’t have it.

The Kentucky company that makes the Intoxilyzer says the code is a trade secret and has refused to release it, thus complicating DWI prosecutions.

“There’s going to be significant difficulty to prosecutors across the state to getting convictions when we can’t utilize evidence to show the levels of the defendant’s intoxication,” said Dakota County Attorney James Backstrom.

“In the short term, it’s going to cause significant problems with holding offenders accountable because of this problem of not being able to obtain this source code.”

Law enforcement officers can still have a motorist’s blood-alcohol level determined through blood tests or urinalysis, but that option comes with a pricey, time-consuming caveat: Most of those tests are done only in the lab run by the Minnesota Bureau of Criminal Apprehension in St. Paul.

“The BCA labs are overwhelmed now with their current workload, and I’m not sure they can handle doing blood and urinalysis tests in all DWI cases in Minnesota,” said Backstrom. “It’s going to be a big problem.”

“I think there’s going to be a lot more blood and urine tests asked for,” said Derek Patrin, an attorney involved in the cases decided by the Supreme Court. “And that will back up the BCA. They’re short-staffed already, and with the budget crisis we’ve got already, well, that’s one of the reasons they wanted to use the Intoxilyzer in the first place. It was inexpensive to use.”

Andy Skoogman, a spokesman for the Department of Public Safety, the BCA’s parent agency, said officials there felt it was “premature” to stop using the Intoxilyzer. But he said the lab would be able to handle the workload if police agencies switched to blood tests and urinalyses.

“The BCA will make adjustments,” he said. “We’ll look at retraining staff and perhaps look at purchasing more test kits until this situation is resolved.”

The Intoxilyzer 5000EN is the standard device used by Minnesota police to determine if a driver is impaired. The state bought 260 of the machines from the manufacturer, CMI of Kentucky, in 1997, and state law presumes the devices’ results to be reliable.

The device is used with nearly eight of every 10 suspected drunken drivers who are tested in Minnesota.

But defense attorneys have argued that if they can’t examine the source code, the computer program that runs the machine, they have no way to tell if the Intoxilyzer is reliable. District judges across Minnesota have handled defense requests for the source code with a patchwork of rulings: Some say a defendant has a right to examine it; others say it isn’t relevant.

The Supreme Court’s ruling came in two driving-while-impaired cases that Backstrom’s office prosecuted. In each, district judges ordered that the source code be turned over to the defendants, but when Backstrom appealed to the Minnesota Court of Appeals, the rulings were overturned.

The appeals court said the defendants hadn’t shown why getting the source code was relevant to their guilt or innocence.

But the Supreme Court said that at least one of those defendants showed that the code was relevant. The court noted in its 18-page ruling a list of evidence that defense attorneys may now use as a blueprint to request the source code.

Police had stopped the defendant, Timothy Arlen Brunner, 38, of Farmington, in July 2007 and the Intoxilyzer showed his blood-alcohol content was 0.18. Minnesota law presumes that a driver with a concentration greater than 0.08 is impaired.

Patrin, his attorney, asked a district judge to order prosecutors to turn over the source code. He accompanied his request with a memorandum and nine exhibits. Among them: a computer science professor’s testimony that defects had been found in the code used in voting machines, as well as a report saying problems had been found in the code used in the breath-testing machine used by police in New Jersey.

The Supreme Court said Brunner’s submissions “show that an analysis of the source code may reveal deficiencies that could challenge the reliability of the Intoxilyzer and, in turn, would relate to Brunner’s guilt or innocence.”

Skoogman, the Department of Public Safety spokesman, said the agency was disappointed in the ruling.

“We feel it is premature at this stage of the game for our law enforcement partners to test for only blood and urine,” Skoogman said. “We continue to stand by the Intoxilyzer and the accuracy of the test results. Our message to law enforcement is to stay the course at this point as we examine our options.”

The state’s access to the source code is the subject of a separate lawsuit in U.S. District Court. Hearings are scheduled in the case May 22 and June 4.

Backstrom said the source code issue would haunt prosecutors until it is resolved, and the Supreme Court decision makes things worse.

“I believe that this decision is a significant setback to law enforcement’s ability to protect our communities from drunk driving, at least in the short term,” he said. “We’re not going to be able to use the Intoxilyzer machine until we get the source code.”

David Hanners can be reached at 612-338-6516.