LOS ANGELES - Pop star Janet Jackson holds Michael Jackson's personal doctor responsible for her brother's sudden death and has told ABC News that a day does not go by when she doesn't think about her late sibling.

"He was the one that was administering," Janet Jackson said about Houston-based physician Dr. Conrad Murray. "I think he is responsible."

Murray, who was hired to treat Michael Jackson in the months before Jackson died on June 25 of a drug overdose, is currently a target in the manslaughter investigation of the "Thriller" singer's death.

Since June, Los Angeles County coroner officials have said the powerful anesthetic propofol, which is used in surgery, and the sedative lorazepam, were the primary drugs responsible for Jackson's death. Police have referred the case to prosecutors to determine if criminal charges should be filed.

Janet Jackson has remained mostly quiet about her brother's death, but she spoke with ABC television journalist Robin Roberts in an interview set to air Wednesday night on the network's show "In the Spotlight."

"It's been a tough year," Jackson told Roberts, in excerpts posted on ABC News' website on Monday. "You have your days where it's just really -- it's hard to believe. And a day doesn't go by that I don't think about him."