After all the search warrants, witness interviews and forensic tests, a team of veteran prosecutors and investigators came to an overwhelming conclusion about the death of Frank Wagner. The industrial explosion that killed him, they agreed, was the result of reckless criminal conduct by his employer, McWane Inc., the Alabama conglomerate that owns a cast-iron foundry here in upstate New York.

''The evidence compels us to act,'' the prosecution team wrote in a confidential memorandum to the state attorney general, Dennis C. Vacco, in 1996. The team urged him to ask a grand jury to indict McWane and its managers on manslaughter and other charges. A grand jury inquiry, senior investigators believed, could have taken them up the corporate ladder.

But Mr. Vacco never sought an indictment against McWane for any crime. Only after an unusual intervention by the United States attorney in Buffalo, who threatened federal charges, did McWane agree to plead guilty to a state felony and pay $500,000. But as the company and Mr. Wagner's widow are quick to note, that charge, a hazardous-waste violation, specifically did not hold McWane accountable for Mr. Wagner's death.

Looking back in bitterness, many of the investigators view the devolution of the Wagner case as the result of a hardball campaign of political interference orchestrated by McWane, one of the world's largest makers of cast-iron sewer and water pipes.