Courts, expert witnesses, prosecutors and defense attorneys in states across America are raising questions about the tests police use to test the alcohol levels of suspected drunk drivers.

Thanks to years of challenges from defense attorneys and judges willing to hear those challenges, surprising and troubling facts about the reliability of government evidence is finally making an impact, according to an investigation by the New York Times.

Keeping methods and machines hidden

In the U.S., a blood alcohol content (BAC) above 0.08% generally means a suspect is not legal to drive. But often, convictions do not come from blood tests. Instead, breath-test machines estimate the suspect’s blood content, and often this is all it takes to get a conviction.

Suspects and their defense attorneys generally have a right to examine the evidence used against their clients. But attorneys repeatedly hit roadblocks when trying to examine these breath-test machines and the software they run on. Manufacturers refuse to sell the machines to the public, including law firms.

When experts do closely examine them, the machines repeatedly turn out to be inaccurate.

Problems revealed by court challenges

For example, it turned out Washington State, chose not to pay for a temperature sensor in its machines. Most breath is well above 93.2 degrees. But that is the highest temperature at which their machines give reliable results without a temperature sensor to adjust the readings.

Florida adopted its breath-test model even after, during a test-drive, it short-circuited and billowed smoked.

When Florida decided alcohol levels from these machines were too low, the company modified them to give higher results. Finding out they had not revealed this modification, a Florida judge wrote, “A criminal defendant should not face conviction and possible incarceration based on secret undisclosed evidence.”

The state forensic lab of Massachusetts had no instructions for setting up and calibrating their machines. One Massachusetts testing machine had a rats’ nest living inside it.

Massachusetts had to throw out tens of thousands of test results, one of the biggest evidence purges in American history. Almost 30,000 people with DUI convictions will be eligible to ask for new trials.

In New Jersey, a similar purge will allow the same chance to 13,000 people.