After the L.A. Coroner examined Jackson's body, his family ordered a second, private autopsy on the singer.
"He had needle marks on his neck and his arms and more about those will emerge in the next few weeks," La Toya Jackson told the Daily Mail.
"I cannot discuss that any further as I may jeopardize the investigation," she said. "I can, however, say that I have not changed my mind about my feeling that Michael was murdered."
La Toya Jackson also said her suspicions were raised by medical equipment, including oxygen tanks and a stand with a cord hanging down, in a room at her brother's home.
Media reports have said that the dangerous sedative Diprivan -- normally used in hospitals by anesthesiologists -- was found at the singer's home.
Los Angeles police have revealed few details of their investigation, and the L.A. Coroner said it will release the results of its autopsy within weeks.