He thought spies hid in the walls of his mansion. He thought he was the Dalai Lama. He rumbled around his vast estate in Newtown Square in a tank.

But the tales we heard about John E. du Pont did not give us the answer we needed. Amid all the bizarre details surrounding his murder of Olympic wrestler David Schultz, one question lingered.

Why did he do it?

From the moment fellow Inquirer reporter Ralph Vigoda and I began covering the homicide by the chemical heir, that was what everyone wanted to know. Why would du Pont, who died in prison Thursday, take the life of his young friend Schultz? And, in the process, throw away his own?

Everyone who became intimate with the case, from police to lawyers to reporters, had a theory. What we never had was an explanation from the man who in January 1996 pulled the trigger of a .44-caliber Smith & Wesson three times.

My association with the case began soon after du Pont fired those shots. Dick Cooper, then an editor at the paper, assigned Vigoda and me to check out a police scanner report of shots fired on the du Pont estate.

I drove to the Newtown Township police station, and Ralph went right to the estate, Foxcatcher Farm. When I joined Ralph at one of the entrances to Foxcatcher, a squad car sat as a barricade.

"Bill, we're going to be here for a while," Ralph said as late afternoon turned to chilly dusk. "I just looked in that cop car, and in the backseat there are doughnuts - a whole box."

Ralph, as usual, was right.

Du Pont, a well-armed marksman, remained holed up inside his mansion as police from across the region, a string of TV trucks with satellite dishes, and a steady stream of the curious held vigil. Meanwhile, we tried to learn about the man inside a house modeled after President James Madison's Montpelier in Virginia.

Two days after the killing, after police had shut off the heat to his house, du Pont was lured outside and captured without a shot being fired.

The ensuing 16 months of court proceedings were filled with convoluted legal machinations and tales of madness. The wealthy defendant's hair grew shaggy, his chin unshaven. He started looking like another better-known recluse - Howard Hughes.

Except for a few words here and there, and an apology at his sentencing, du Pont remained a sphinx.

His lawyer, Thomas Bergstrom, tried to get jurors to find his client not guilty by reason of insanity. And if they, too, found it difficult to fathom a reason for the killing, it was because there was none.

"He was simply sick," Bergstrom said.

In the end, prosecutors Joe McGettigan and Dennis McAndrews won the day, carefully building a case that du Pont, while mentally ill, was sane enough to be held responsible for his actions.

McGettigan argued that du Pont had been fueled by envy and a misplaced sense of betrayal because Schultz had been preparing to leave the estate to try out for the 1996 Olympics.

McAndrews, whom McGettigan still credits with doing the scholarly mental-health work on the complex case, argued that du Pont was not nearly as crazy as he wanted jurors to believe, that he was "a fraud - a colossal fraud."

Maybe so. But to those of us who kept a vigil outside that Madisonian mansion and tried to discern the motives of the man inside, something du Pont's own lawyer told the jury still rings true.

"There was a full moon at Foxcatcher," Bergstrom said, "every night of the week."

Former Inquirer staff writer Bill Ordine and his late colleague Ralph Vigoda wrote "Fatal Match," a book about John E. du Pont and the slaying of David Schultz.