Green’s Dictionary of Slang

garreter n.

also garreteer
[SE garret + sfx -er, doer, agent; cit. 1890 prob. mis-spelling]

(UK Und.) a thief who crawls over house-tops and breaks in through garret windows.

[UK]Hotten Sl. Dict. 141: garreter a thief who crawls over the tops of houses, and enters garret-windows.
[Aus]Australiasian (Melbourne) 17 July 8/5: A man who gets over roofs or in at windows is called a garreter and a dancer.
[UK]Sl. Dict.
[UK]Clarkson & Richardson Police! 260: About 40 were burglars, ‘dancers,’ ‘garreters,’ and others adept with the skeleton keys.
[UK]Farmer & Henley Sl. and Its Analogues III 120/2: Garreteer subs. (thieves’) A thief whose speciality is to rob houses by entering sky-lights or garret-windows.