Companions in Nightmare

Companions in Nightmare is a 1968 crime-drama film. It had early roles for Louis Gossett Jr. and Bettye Ackerman, and it also starred Gig Young, Melvyn Douglas, Patrick O'Neal and Leslie Nielsen.
Plot.
Dr. Lawrence Strelson (Melvyn Douglas) is a famous psychiatrist who conducts a group-therapy session with several high-priced professionals. It turns out that one of the patients is a murderer; the truth will come out, and it will be a shocker. Among the special guest suspects are Eric Nicholson (Gig Young), Carlotta Mauridge (Anne Baxter), Jeremy Siddack (Patrick O'Neal), Julie Klanton (Dana Wynter) and Dr. Neesden (Leslie Nielsen).