skylarker, n. — Green’s Dictionary of Slang

skylarker n.

[using the legitimate job to facilitate the villainy, he gets up early – ‘with the lark’ – to spy out vulnerable houses]

a thief who doubles as a journeyman bricklayer; thus skylarking n., thieving in this manner.

1789		G. Parker Life’s Painter 170: The sky-larker is a thief, and will rob the house somehow or other, by slipping into some of the chambers, &c.
1801		G. Hangar Life, Adventures and Opinions II 60: Various impositions, practised daily on the unwary [...] such as the running rumbler, skylarking, blue pigeon flying.