Do I have a malpractice claim in the death of my mother?

My mother passed away in a rehab center at the age of 91. Prior to her admittance for a broken leg, she was in excellent health. After she passed away, my sister, also a doctor, told me she felt the doctor who saw my mother in the rehab center contributed to her death. My sister stated the doctor had switched my mother's medications around in such a way that they were not constant as they needed to be. I also know about two other patients whose families were so concerned over this doctor's treatment of their family members, they had him removed from their cases. One of these had a friend who was a nurse, who was so concerned over the patient's care, she felt the patient's life was in danger. While I do not know that this doctor's care killed my mother, I certainly believe it contributed to her death. I am wondering if this would constitute a malpractice lawsuit.