Green’s Dictionary of Slang

to execute, to murder.

1850		E.V. Kenealy Goethe: a New Pantomime 271: Down in the waves of human blood, lie stretched / Mixed with the shabbiest creatures e’er Jack Ketched.
1853		Bell’s Life in Sydney 17 Sept. 2/7: Them ere fowls was all live and in good health last night, but now they’ve been regularly Jack Ketched.
1877		Reynolds’s Newspaper 9 Dec. 5/2: Three men were ‘Jack Ketched’ for causing the death of an old man in a drunken brawl.
1879		Fun 272: If the abusers of ankle jacks were occasionally Jack Ketched, universal gloom would not swallow up the community.