Jackson, who died June 25 after suffering cardiac arrest at the age of 50, was briefly married to, then divorced from, Presley's daughter, Lisa Marie.
Jackson's private doctor, Conrad Murray, has been interviewed by police and his home, offices and storage unit searched. Law enforcement sources reportedly said Murray is believed to have administered anesthesia to Jackson at the singer's Los Angeles home shortly before the entertainer died.
Elvis Presley died in 1977 of a heart attack at the age of 42 after years of abusing prescription drugs.
Dr. George Nichopoulos, 82, in his new book, "The King and Dr. Nick," due out in February, explains how he doesn't want his grandchildren to grow up regarding him as being responsible for Presley's death, the Memphis Commercial Appeal reported.
"I don't regret any of the medications I gave him. They were necessities," Nichopoulos told TV's "Entertainment Tonight" of the drugs he prescribed Presley.
Nichopoulos was acquitted decades ago of charges he overprescribed drugs to Presley, Jerry Lee Lewis and seven others, the Commercial Appeal said. Nichopoulos also dodged comparisons between the Presley and Jackson cases during his "Entertainment Tonight" interview.