'You know what's amazing to me? Somehow it all comes back to Danny Keeler.'

As a lead homicide detective in Boston for 12 years, Sergeant Daniel M. Keeler weathered plenty of storms: a wrongful conviction of a murder defendant, a furor over his shooting a former convict in the head, and his outburst at a federal prosecutor, to name a few.

But last year was particularly turbulent for the hard-driving and controversial former Marine whose work on more than 200 murder cases earned him the moniker Mr. Homicide.

In the span of nine months, prosecutors dropped a murder charge against a Revere man who said Keeler railroaded him, jurors blasted his investigative tactics in a separate homicide case, and the detective admitted on the witness stand in another high-profile trial that his police report contained false statements.

Today, the 53-year-old detective will again find himself under attack in a courtroom, but under strikingly different circumstances: He's being sued for slander by Stephen Hrones, a high-profile defense lawyer and longtime antagonist.

The trial will return the spotlight to Keeler, a 26-year veteran officer who says he's been unfairly maligned by defense lawyers, defendants, reporters, and people who don't understand police work.

"You know what's amazing to me?" Keeler said recently, his accent full of his Dorchester roots. "Somehow it all comes back to Danny Keeler."

Keeler left the homicide unit last spring, but remains a fixture at the Suffolk County courthouse as he testifies in numerous murder cases wending their way through the courts.

His is a commanding presence. Muscular, he strides purposefully through the corridors in sharp-looking suits. He can be seen telling families enraged when loved ones are convicted to show dignity. He testifies so often that he addresses jurors with the poise of a talk-show host facing his studio audience.

But he is a polarizing figure.

Admirers call him an indefatigable and compassionate detective with superb crime-fighting instincts.

Former Suffolk district attorney Ralph C. Martin II said Keeler "was respected for his work ethic and for his doggedness and his sort of willingness to look everywhere, look at every angle."

Defense lawyer Roger Witkin calls him one of the most intuitive cops he has ever met.

Critics charge that Keeler is an overzealous, self-righteous officer who twists facts and cuts corners to close murder cases, sometimes at the risk of arresting the wrong man.

Defense lawyer Rosemary C. Scapicchio, who represented James Bush when he was acquitted in November of murdering 3-year-old Malik Andrade Percival after Keeler conceded his police report contained inaccuracies, said Keeler refuses to consider other leads once he homes in on a suspect.

"He determines very quickly who he thinks did it, and . . . if there are other potential suspects out there, those leads are never followed up on," Scapicchio said.

Keeler called Scapicchio's criticism "nothing short of outrageous."

Although several defense lawyers assail Keeler's police work, no one is as outspoken as Hrones, who seems practically giddy that his suit is going to trial.

Hrones, every bit as aggressive and controversial as Keeler, contends that the detective falsely accused him of lying to the state's highest court in 1998 while arguing for a new trial for his client, Donnell Johnson. Johnson was convicted in a 1994 murder, but was exonerated after serving five years in prison.

In arguments before the Supreme Judicial Court, Hrones said a colleague of Keeler's in the homicide unit committed perjury. Keeler responded in a Globe story that Hrones was "misrepresenting the truth, and he knows it."

Legal specialists say Hrones could face long odds, in part because he never specified how his reputation was damaged. The Suffolk Superior Court trial starts this morning.Keeler declined to comment on the merits of Hrones's lawsuit. But he has said in recent months that he is a victim of a smear campaign by Hrones and Scapicchio and by defendants utterly lacking credibility.

Born in Quincy and reared in Dorchester, Keeler attended Boston Technical High School, spent two years in the Marines, and joined the Boston police in 1979. The young patrolman made headlines just a year later when he jumped 60 feet from the Boston University Bridge to save a man who had jumped into the Charles River in an apparent suicide attempt.

In 1992, he joined the homicide unit and quickly gained attention for helping to close murder cases, including one that had been unsolved for 25 years. He also developed a tough-talking, slang-driven style of interrogating suspects that could make even the hardest-boiled television detective sound genteel.

As the head of a squad that included two other detectives, Keeler worked long hours investigating crimes and testifying. He earned $150,689 in 2003, $88,830 of it in overtime.

He also earned praise from relatives of crime victims.

Charlette Robichaud, whose 19-year-old brother-in-law was fatally stabbed in 2001, said Keeler can be blustery but added: "Would you want someone who's soft or easygoing investigating the murder of your child? You want someone who is going to be determined to go after the truth, and that's what he is."

Detractors have accused Keeler of being a cowboy who believes the ends justify the means.

In a federal lawsuit Johnson filed after he was freed, he contended that Keeler and another detective buried evidence that could have cleared him. A judge dismissed the suit last year, but said the allegations were "deeply troubling."

Keeler also drew rebukes from some Boston residents for shooting a suspect in the head during a gun battle at a Roxbury intersection in 2002, a shooting investigators later deemed justified.

Last year was particularly rocky for Keeler. First, Suffolk County prosecutors cleared William Leyden of committing the 2001 decapitation murder of his brother, John "Jackie" Leyden. Keeler had speculated on the ABC series "Boston 24/7" about why Leyden killed his brother.

Then a jury stunned prosecutors in April by acquitting Kyle Bryant of murdering his 14-year-old girlfriend and her unborn child in 1999, even though he had told Keeler in a tape-recorded statement that he was present when she was killed.

Afterward, a juror accused Keeler of "haranguing" Bryant in the interrogation.

And then James Bush was acquitted in Percival's murder after Scapicchio successfully accused Keeler of sloppy police work.

Through it all, Keeler -- who can sound surprisingly thin-skinned, given his line of work -- vigorously defended his record.

He said Leyden was charged largely on the basis of DNA evidence before someone else confessed to the crime. He said his demeanor in Bryant's interrogation was warranted, given the gruesomeness of Jones's murder. And he faulted Suffolk prosecutors for failing to win convictions.

In the spring, Keeler was transferred to a night-shift assignment in the South End and Back Bay. Police Superintendent Paul Joyce said Keeler voluntarily made the move after spending 12 years giving "100 percent to the department, to the homicide unit, and to the families of homicide victims."

Keeler said that it was time to move on.

"If you've seen 12 years of bodies," he said. "Enough was enough. You don't leave that at night and then go home and sleep as others do. But to have my character called into question? That causes pain, too."