An 87-year-old woman confessed to the police that she gave her 30-year-old grandson a fatal dose of the drug because he feared that when he died there would be no one to take care of him.
Joel Parks lived in a residence on weekdays and with her grandmother on weekends. It was on Sunday that his visiting sister found him dead.
When authorities arrived, her grandmother, Lillian Parks, admitted that she had killed her disabled grandson and couldn't take care of himself, said Bradenton, Florida police spokesman.
It is not known if Lillian, who is now in a medical facility, believed she was going to die soon to have committed the crime, but when the doctors discharge her, she will have to go to court.
"This is a difficult case, partly because we feel bad for an individual who feels that the only option is to take another human being's life because he is so worried about who will take care of him," said Thiers. "But on the other hand, this is a process that has been designed and planned to kill a person. We need to do everything we can to bring justice to their family."
Police spokesman did not say that drugs Lillian was used to kill Joel, while still awaiting the toxicology report and medical examination, but stressed that the woman could be charged with second-degree murder.