Two days after the Memphis police declared Loeb Professor of Biophysics and Biochemistry Don C. Wiley likely to have committed suicide, colleagues of the professor, now missing for 15 days, have expressed doubt that he took his own life.

Hidde Ploegh, Mallinckrodt professor of immunopathology, said that despite the police department’s statements yesterday, he is not convinced that Wiley committed suicide.

“What the police say is one thing, and what happened, I don’t think anyone knows,” he said. “I think there are no new facts to shed light on [the situation] and anything people add should be labeled as speculation.”

Since Wiley’s disappearance, rumors have circulated that he was perhaps distraught about not winning the Nobel Prize in 1996, when two scientists working on similar research received the award.

Jack L. Strominger, Higgins professor of biochemistry at Harvard who shared the Lasker Award in 1995 and the Japan Prize in 1999 with Wiley, said that “from everything I know, there is no possibility that he committed suicide.”

The Lasker Award is awarded to clinical scientists annually and is considered “a precursor to receiving the Nobel Prize,” said Philippa Marrack, a professor of immunology at the National Jewish Medical Center and an investigator with Wiley for the Howard Hughes Medical Institute.

Since 1962, more than half of those who won the Lasker Award went on to receive the Nobel Prize, most within two years of receiving the Lasker.

The year after Wiley received the Lasker Award, the Nobel Prize went to scientists Peter Doherty and Rolf Zinkerngel who had shared the Lasker Award with Wiley in 1995.

They had done earlier but similar work to Wiley’s on immunology, said William Evans, deputy director at St. Jude’s Hospital which hosted the banquet in Memphis where Wiley was last seen.

A total of five people, including Wiley, were conducting the research, and only two of the five were awarded the Nobel Prize.

Marrack said she believes Wiley knew why the two recipients were selected.

“The Nobel Prize that year was given for biological discoveries rather than the structural solutions [which Wiley worked with],” said Marrack, a colleague of Wiley’s for more than 15 years.

Marrack said she never discussed the 1996 Nobel Prize with Wiley but emphasized that he wasn’t the only candidate not to receive the Nobel Prize that year.

“It wasn’t just Don Wiley; there were others, and they didn’t throw themselves off bridges,” said Marrack.

Marrack said she does not believe Wiley committed suicide.

“He didn’t seem to be a person who would do that, not under any circumstances, and especially in his father’s town. He cared about his family,” she said.

James Davis, a colleague of Wiley’s and head tutor for the Chemistry Department, said he doesn’t “know anymore what to think.”

“I walked across campus with Don three weeks ago, and he seemed as cheery-eyed as ever,” he said. “I’m mystified. It’s extremely hard to believe that he would take his own life, given what people know about his personality and sunny disposition.”

Evans said that at the conference in Memphis where Wiley was last seen the scientists did not discuss this year’s Nobel Prizes, whose recipients have already been announced and will receive their awards on Dec. 10 in Stockholm.