The wife of the man I had come to visit came to the door, and when I told her what I wanted to see him about, she said: “I wish you wouldn’t. It’s very painful. The kids don’t know about this.”

She went to find him, the main person of interest.

Those at Cornell found him strange. Awkward, standoffish, impossible to penetrate. Mr. Freeman, the family medicine physician, recalled him as a “mama’s boy type” who adjusted imperfectly to college. No one, though, seemed to know anything about his grades. He stayed up late playing bridge, as did Mr. Freeman. “I don’t remember him saying much other than, ‘I bid two clubs,’” he said.

In 1966, Mr. Heumann, the technical writer, accompanied him to his family’s Brooklyn home for Thanksgiving. He recalls odd exchanges. His father, a garment worker, mentioned how disappointed he was with his son. At his age, he said, he was running all over New York having a grand time. Sadly, his son wasn’t adventuresome.

Two months before the Res Club fire, the man and some classmates painted a house for a family who had been burned out in a pre-dawn fire.

What else is known?

In a police document harvested by Mr. Fogle, David Katz, a first-year Phud, told an investigator that he had seen the man playing with matches and saw matches and caps for a toy pistol in his suitcase. He also told the police that the man lied about being at home on Eddy Street (the location of the third fire) the night of the Watermargin fire, because he looked for him and couldn’t find him. He discovered the shower running in an empty bathroom. In the police file is a letter the man’s mother wrote to Cornell saying that her son was under immense pressure and having difficulties and needed a break.

Mr. Showalter told me that he reported to the police that he and other Phuds suspected him of setting the minor fires that preceded the fatal fire, since they had seen him fooling with matches. “I mentioned that to him and he said emphatically, at the top of his lungs, ‘That’s a terrible thing to say about anybody,’” Mr. Showalter said. After Watermargin, according to police records, the man declined to take a lie-detector test or talk to the police without a lawyer.

And the new identity. The man told the State Police in 2015 that he changed his name because of friction with his parents and wanted to disconnect from them and not be found. The officer, according to a fellow investigator, didn’t believe him. It would have been unusual to do so at age 19. And the man had visited his family since then.