Arnold Klein, one of Hollywood’s star dermatologists and a doctor for Michael Jackson for nearly 25 years, was apparently forced to leave his residency at the Hospital of the University of Pennsylvania in the 1970s because of allegations that he was selling unauthorized prescription drugs to fellow students, according to two people who know him.

The Daily Beast has confirmed that Klein is one of the doctors being investigated by authorities in connection with Jackson’s apparent drug overdose. These allegations raise questions about his attitude toward prescription drugs, and also whether Klein would have been licensed for practicing medicine had Penn authorities shared the information with law enforcement or the California medical-licensing boards, the state to which Klein moved and established his tremendously successful practice.

Klein’s colleagues recalled that when he left for California, there was no indication of wrongdoing, but that he told them he was moving to the West Coast because he was about to become engaged to a woman who lived in Los Angeles (Klein has never married).

Walter Shelley, the former chairman of Penn’s Dermatology Department, where Klein had his residency, often told colleagues about the incident (Shelley passed away this past February at age 91). Two of those doctors, familiar with the account as related by Shelley, spoke to me, and independent of each other, verified the same information. Shelley told them separately that Klein’s residency had been terminated because he had sold prescription meds to other students. The Hospital at the University of Pennsylvania, Shelley told them, agreed not to turn the information over to local authorities in return for Klein leaving the school. He did so, completing his residency at the University of California at Los Angeles, where he was the chief resident in dermatology in 1975.

Klein’s colleagues recalled that when he left for California, there was no indication of wrongdoing, but that he told them he was moving to the West Coast because he was about to become engaged to a woman who lived in Los Angeles (Klein has never married).

One of Klein’s Penn colleagues thought that Klein might have been influenced by a book he cowrote, Drug Trip Abroad: American Drug-Refugees in Amsterdam and London, which was published by the University of Pennsylvania Press in 1972, a year after Klein graduated cum laude and Phi Beta Kappa from the University of Pennsylvania School of Medicine. Shelley said he believed that Klein had obtained his medications from Mexico.

“That book immersed him in the drug world,” a fellow physician told me. “It might have been the catalyst for what got him into trouble with the school administration.”

Klein’s attorney, Richard Charnley, did not reply to two emails, setting forth the details of what The Daily Beast had learned about Klein and his residency problems. I telephoned Charnley and left a detailed message, offering Klein the opportunity to rebut or answer the substance of these new revelations, but Charnley again did not respond. I also telephoned Klein’s office directly and spoke to a receptionist at length. I did not receive a return call. Administrators and lawyers at the University of Pennsylvania Health System, which covers the hospital at which Klein was a resident, declined to comment on why Klein left Penn.

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Gerald Posner is The Daily Beast's chief investigative reporter. He's the award-winning author of 10 investigative nonfiction bestsellers, ranging from political assassinations, to Nazi war criminals, to 9/11, to terrorism. He lives in Miami Beach with his wife, the author Trisha Posner.