Janet Jackson blames Dr. Conrad Murray for her brother's June death from lethal levels of the powerful sedative propofol.

"He was the one that was administering," she tells Robin Roberts on ABC News' "In the Spotlight" in an interview to air Wednesday. "I think he is responsible."

Murray is currently under investigation in Michael's June death, which was ruled a homicide.

Janet -- who will open the American Music Awards later this month -- admits it's "been a tough year.

"You have your days where it's just really -- it's hard to believe," she says. "And a day doesn't go by that I don't think about him."

Janet says the day Michael died started like just "another day... another morning."

"I was at my house in New York ... And I get a call ... [my assistant] said, 'Your brother's been taken to the hospital. It's on CNN right now,'" she says. "I called everyone. There's a line busy or -- someone wasn't picking up. I spoke to mother. I spoke to [brother] Tito. I spoke to my nephew Austin. I spoke to my sister La Toya."

Janet goes on, "I told them to call me when they got to the hospital," she goes on. "And I remember thinking nobody's calling me back, so I tried calling again, and that's how I found out that he was no longer ... I couldn't believe it."

When she heard he died, she was in shock.

"It just didn't ring true to me," she says. "It felt like a dream."

It's "still so difficult for me to believe," she admits. "It's, you know, you have to accept what is. But it's hard. You have to move on with your life. You have to accept what is and I understand that."

She hadn't hung out with her brother since two days before her 43rd birthday in May.

"We had a lot of fun, laughing... I was being silly, acting silly," she says. "And he was sitting in front of me and just cracking up, laughing at me. I was being loud. And he thought it was so funny. I was just being stupid, acting silly."

Attending Michael's July memorial at Los Angeles' Staples Center -- where he had rehearsed for his comeback tour, This Is It -- helped her cope with the loss, she says.

"My brother's favorite song is 'Smile.' And I thought Jermaine sang it beautifully, beautifully," she says. "And that's his favorite song as well. ...There being some sort of a closure, I suppose."