The autograph of the Requiem was placed on display at the World's Fair in 1958 in Brussels.
At some point during the fair, someone was able to gain access to the manuscript, tearing off the bottom right-hand corner of the second to last page (folio 99r/45r), containing the words "Quam olim d: C:" (an instruction that the "Quam olim" fugue of the Domine Jesu was to be repeated da capo, at the end of the Hostias).
The perpetrator has not been identified and the fragment has not been recovered.

If the most common authorship theory is true, then "Quam olim d: C:" might very well be the last words Mozart wrote before he died.
It is probable that whoever stole the fragment believed that to be the case.
The autograph of the Requiem was placed on display at the World's Fair in 1958 in Brussels. At some point during the fair, someone was able to gain access to the manuscript, tearing off the bottom right-hand corner of the second to last page (folio 99r/45r), containing the words "Quam olim d: C:" (an instruction that the "Quam olim" fugue of the Domine Jesu was to be repeated da capo, at the end of the Hostias). The perpetrator has not been identified and the fragment has not been recovered.
If the most common authorship theory is true, then "Quam olim d: C:" might very well be the last words Mozart wrote before he died. It is probable that whoever stole the fragment believed that to be the case.
Requiem (Mozart)