I am well-versed in psychology and mental health and I understand the effects medication can have. That was my impression as well. There are medications that can make someone extremely calm, passive, emotionally flat and significantly reduce anxiety. I wouldn’t be surprised if LD also took something to help manage his anxiety before the interview (if he is truly guilty).I thought the same thing about MD when she said she hadn't met her. My impression was she seemed very medicated.
Additionally, police may release someone if they do not have enough evidence to hold or charge them. So just because someone is released does not mean they are not guilty of the crime.