Green’s Dictionary of Slang

1. any device (or person) used to extract information from a third party.

1811		Sporting Mag. XXXVIII 168/2: The pretended flat who was a draw, was introduced, and we won five hundred pounds from him .
1818		W. Perry London Guide.
1861		(con. 15C) C. Reade Cloister and Hearth (1864) I 45: This was what in modern days is called a draw. It was a guess, put boldly forth as fact, to elicit by the young man’s answer whether he had been there lately or not.

2. (UK Und.) whatever a pickpocket extracts from a victim.

1853

Chester Chron. 25 June 6/6: ‘Busmobs’[...] are accompanied by lads called ‘Wires,’ whose peculiar avocation it is to pick as many pockets as they can and ‘to pass’ the ‘draws’ to the ‘busmobs’ who have capacious pockets for storing away the spoil.

3. the person from whom the information may be extracted.

1887

‘A Plain Woman’ Poor Nellie (2013) 229: Butt was a sure ‘draw’ on this subject .