From Wiki:
On the evening of May 29, 1997, Buckley's band flew to Memphis intending to join him in his studio there to work on the newly written material. That same evening, Buckley went swimming in Wolf River Harbor, a slack water channel of the Mississippi River, while wearing boots and all of his clothing, and singing the chorus of the song "Whole Lotta Love" by Led Zeppelin. Buckley had gone swimming there several times before. A roadie in Buckley's band, Keith Foti, remained on shore.
So how many completely sober/drug free 30 year olds do you know who swim with their clothes on, let alone boots? Seems highly suspicious.