In her quest to find the truth about what happened to her late mother, Joan Rivers, Melissa Rivers has another victory under her belt.

New testimony in Melissa’s multimillion-dollar lawsuit against the medical practice that treated Joan bolsters the claim that the comedienne’s doctor took pictures of her while she was under sedation during a surgical procedure that ultimately killed her last year.

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Joan in 2014.

The filings include corroborating accounts from multiple employees of Yorkville Endoscopy in NYC that Dr. Lawrence Cohen took the photos.

RELATED: Melissa Rivers Opens Up About What Went Wrong On ‘Fashion Police’ After Joan Rivers’ Death

Medical malpractice expert Michael Lamonsoff tells Closer these witnesses bolster Melissa’s case. “People have an expectation that when they go in for surgery the doctors will not deviate from the accepted standard of care,” he says. “Such unprofessional behavior created a hotbed of distraction, ripe for potential errors and mistakes.”

Dr. Cohen has denied he took the pictures, but now may be forced to answer the charges under

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Joan and Melissa in 1970.

To read the full story on Joan and Melissa, pick up the new issue of ‘Closer Weekly’ on newsstands now!