On the show I went to Sufjan said it was an albino rat who got beat to death in a coffee can with a baseball bat (and I think he said his name was Mr. Buttons or something). Sufjan's stories are like the murder cards from the board game Clue that he mixes up to make something different every time. The albino salamander, in the backyard, with the hammer!
Some say Cat Stevens because of his last name. I say PAul Simon's grandson because Paul hitch hiked from Saginaw back in the sixties. Well you never know. I love this guy!
The whole thing with reincarnations is impossible since more humans are alive today than have ever existed in the history of mankind. So yeah, the math doesn't add up.