The jury’s verdict came after its members heard descriptions of Mr. Blankenship’s fortune — he was paid nearly $18 million in 2009, the last full year before the explosion at the mine just about everyone called “U.B.B.” — and saw documents that portrayed him as a manager with sophisticated knowledge of his multibillion-dollar corporation. Jurors learned about his demands for production reports from Upper Big Branch every 30 minutes, even on weekends, and they heard him, on audio recordings, chastising and lecturing subordinates.

Perhaps most crucially, they heard dueling interpretations of an array of memos and programs about safety at Massey, a company that had thousands of safety citations and, according to the government, embarked on little more than a safety charade.

Mr. Blankenship’s lawyers, however, said that prosecutors had stretched federal laws and the evidence to their limits in their quest to prosecute Mr. Blankenship, a Republican who has suggested that the case against him was a form of political retaliation.

“Nobody’s blaming the miners,” Mr. Taylor said during his closing argument last month. “But the government wants you to find beyond a reasonable doubt that Don Blankenship is a criminal because this mine got citations.”

On Thursday, as he had for months, Mr. Taylor said that the case should have never been brought. But prosecutors, in interviews during the jury’s deliberations, defended their approach in a wide-ranging inquiry that began soon after the disaster and, ultimately, amassed a varied record.

“If we were going to have a shot at who, if anyone, was responsible for the circumstances that might have contributed to this event, then we would need to investigate this like we investigate criminal cases,” said R. Booth Goodwin II, the United States attorney. “How is it that this happens, and how is it that we have what seemed like a Third World mine disaster in the 21st century here in America?”

Last November, almost three years after the company that bought Massey agreed to a $209 million settlement with the Justice Department, a grand jury indicted Mr. Blankenship. He assembled a roster of lawyers for a defense that cost millions of dollars, while prosecutors weighed how to present a complicated case. Unlike the prosecutors, Mr. Taylor would not agree to discuss how the case unfolded.