Authorities do not know whether Haim filled the prescription or if someone was using his name, investigator Javier Salaiz told The Associated Press.
Shepis said Haim often talked about wanting to get clean.
"Unfortunately, I think, you really only have to want to do that for yourself. Nobody can take you by the hand and make you do anything," she said. "He was too far into it, I think."
The Associated Press contributed to this report.