Meier earned his legal degree from Boston University School of Law in 1981. One of his acquaintances there was the acclaimed screenwriter-producer David E. Kelley, who has often used the names — if not the spirits — of former law school pals as the basis for characters. L.A. Law fans may recall an irksome direct-mail magnate named Dave Meyer, played by the actor Dann Florek.

After law school, Meier was hired as a rookie assistant district attorney in Middlesex County, assigned to Framingham District Court. It became his training ground. In Framingham and later in Cambridge, he tried hundreds of cases in front of juries. Meier developed a persuasive trial demeanor, more methodical than histrionic. “He made it seem as though there was only one possible reasonable answer, and it was a one-word answer starting with a ‘g,’ ” says retired Superior Court judge Hiller Zobel.

As he moved up the ranks, Meier began to see glimmers of injustice. “I remember feeling some unease at times with the pressures that were put upon you as a prosecutor,” he says. Lawyers on both sides of a trial have a tendency to “treat facts as tools you use in your cases,” says Marty Murphy, a friend and prominent Boston lawyer who worked with Meier in the Middlesex DA’s office. Meier bristled at that. He was, Murphy says, “obsessively concerned about the facts,” insistent that they not be manipulated, ignored, or purposefully omitted, even when they might be inconvenient to your side.

In 1989, Meier’s principles were put to the test. About 18 months earlier, a man named Calvin Reid had been arrested for allegedly breaking into the Somerville house of a young couple, raping the pregnant wife, and then making off in their car with a TV, VCR, and stereo. Meier took over the case as the trial approached. Once he dug in, he developed grave concerns about the evidence and about how Reid had been identified. So he laid them out over several hours one Saturday morning to his boss, Tom Reilly, then the first assistant district attorney in Middlesex. Meier wanted to send the wife’s sweat pants out for DNA testing, which at the time was novel — and expensive. Reilly agreed.

When the results came back, they pointed to another man’s DNA, excluding Reid as a suspect. Had Meier just pushed on, it’s conceivable, if not likely, that he could have convicted Calvin Reid. It was a watershed moment for Meier. He had trusted his gut, and his gut had been right. “The ethical commitment to doing the right thing was there from the beginning,” Reilly says. “You didn’t have to instill that in David.”

This sensibility helped make Meier a prime recruit when the Suffolk County district attorney, Ralph C. Martin II, needed a chief of homicide in 1996. Over breakfast at Charlie’s Sandwich Shoppe in the South End, the deal was sealed: Meier would come to Boston and help Martin launch a new era of cooperation between the DA’s office and Boston police, in which prosecutors and cops would, in a break from recent practice, work side by side from the start of major homicide investigations. Though there was some resistance in the police ranks to working more closely with prosecutors, Meier helped define a more productive relationship. “He cared about the city, and he cared about the Police Department, and he cared about getting his cases done,” says Paul Farrahar, who commanded the Boston police homicide unit at the time.