Tony Johnson says his sister takes medication to prevent seizures, medication that makes her so weak she frequently falls.
But police say Wednesday Robin Johnson grabbed Officer Francis' gun during a struggle and shot him.
Her brother says she was scared of guns. He said he finds it hard to believe she'd even touch one..
Tony Johson had a message for the officer's family.
"I don't exactly what really happened, but I am extremely sorry for whatever happened to him because his life was taken in the midst of all of this," he said.
Robin Johnson was shot by police and is hospitalized in critical condition. Her brother said he has not seen or spoken to her.