Green’s Dictionary of Slang

absentee n.

[? because he is absent from everyday life]

(Aus./S.Afr.) a convict.

J. Mudie Felonry of New South Wales vii: The ludicrous and affected philanthropy [...] in advertising runaway convicts under the soft and gentle name of absentees.
[Aus]G.H. Lawson Dict. of Aus. Words And Terms [Internet] ABSENTEE — Euphemistic term for convict. Word now disappeared.
[SA]L.F. Freed Crime in S. Afr. 107: A ‘canary bird’ or ‘absentee’ is a convict.