Jermaine Jackson claims his brother Michael went from "good health to death in the space of one day".
The former Jackson 5 bassist is very suspicious of how his sibling died but is hopeful the truth will eventually be revealed.
Michael passed away from a suspected cardiac arrest last month after apparently taking prescription drugs, including powerful painkiller Demerol and anesthetic Propofol.
His personal physician Dr. Conrad Murray was with him at the time of his death.
Jermaine said: "A doctor is supposed to keep someone healthy - but Michael went from good health to death in the space of one day.
"I feel that God put Michael here to do good and he's not going to leave that chapter unfinished.
"I really feel at the end of the day there will be clarity as to what happened. What we don't want and what I can't have is for Michael's passing to be a mystery forever."
Jermaine, 54, also revealed the anger he felt towards Dr Murray - who made an attempt to revive the 'Bad' singer - when he spoke to him in the aftermath.
Police have questioned the doctor since Michael's tragic death to determine what drugs he was prescribing him.
Jermaine added: "The first time I met Dr. Murray was at the hospital. I felt that if he was a doctor, why was Michael not here? Why was Michael dead? I haven't heard any toxicology reports yet and I wouldn't call it anything until we find out what the reports say, until the conclusion of the investigation. The doctors need to be looked at, I did not know these guys, but I'm sure they are all under investigation."
Jermaine was told his beloved brother had died by their mother Katherine as he rushed to the UCLA Medical Center, in Los Angeles, and he admits he was left totally in shock.
He told Britain's The Sun newspaper: "When I called my mother back she just said, 'He's dead.' I'll never forget the tone of her voice - I've never heard that tone before. It was just awful, I just broke down in tears I got there as fast as I could. The security let us through and, once I got inside, I went to the emergency part. Then it hit me. It hit me I had lost my brother and what we had all fought for - the unity. I just said, 'Michael, what do you want me to do? Michael I love you and I miss you so much. Why did you go?' I found myself talking to him in the sky. It's a strange thing, but I feel he's everywhere. His message is so powerful."