Baltimore police Commissioner Frederick H. Bealefeld III said the 50-year-old man was talking to a doctor about his mother when he "became emotionally distraught and reacted ... and was overwhelmed by the news of his mother's condition."
Officials said Davis shot the doctor in the stomach. The shooting was reported just after 11 a.m. ET.
Davis was holed up inside his mother's room for more than two hours during a standoff with authorities.
When officers went up to the room on the eighth floor of the main hospital tower, they found Davis dead on the floor and his mother dead in her hospital bed.
The wounded doctor, who was identified to ABC News as Dr. David Cohen, was rushed to surgery and was expected to survive.
A small section of the hospital was shut down, as police in riot gear moved in.
According to the hospital website, Cohen specializes in spine surgery, osteoporosis and scoliosis.
Police have not confirmed if the doctor and gunman knew each other, but a worker in the hospital said the suspect had complained to other employees that the doctor had mistreated his mother and left her paralyzed.
The Associated Press contributed to this report.
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