As the documents poured in, I knew I needed guides. Lots of people were experts on the issues in their own city or state, but for a nationwide look I needed sources with a broader field of vision who could help me navigate all the rulings and records and focus on the details that mattered most. “Call Tom Workman,” several people told me.

His name turned up in cases all over the country as a witness with an unusual dual-expertise: He had worked for technology companies for two decades as an electrical engineer and software developer, then returned to school and picked up a law degree.

When I got Mr. Workman on the phone, he explained how the inner workings of breath-testing machines had become his career-consuming obsession. A smattering of lawsuits around the country seeking access to the source code of breath-testing machines had caught his eye. When he talked to the lawyers behind those challenges, he became hooked. The issue was high-stakes — a conviction for drunken driving is usually life-altering — and complex.

“When you find a problem in the source code, it’s very difficult to explain the consequences of that problem to a judge or jury,” he told me. “It’s written in a foreign language, and the effects are hard to trace. We’re rarely able to say, ‘Aha, here’s this person’s breath test and here’s the problem that caused it to be wrong.’”