Sources:
The Last Days of John Lennon, by James Patterson with Casey Sherman and Dave Wedge
John Lennon: The Life, by Philip Norman
The Lives of John Lennon, by Albert Goldman
All We Are Saying, by David Sheff
John Lennon: The Rolling Stone Interview (Part One) (Rolling Stone)
John Lennon: The Rolling Stone Interview (Part Two) (Rolling Stone)
Nilsson: The Life of a Singer-Songwriter, by Alyn Shipton
Sticky Fingers: The Life and Times of Jann Wenner and Rolling Stone Magazine, by Joe Hagan
Harry Nilsson Interviewed by DJ Pete Fornatale in 1992 (YouTube)
Deconstructing Harry (Grantland)
Bio Bares the Secret Life of John Lennon (NY Post)
A New Generation Discovers the Music of Elvis Presley (How Stuff Works)