Green’s Dictionary of Slang

fake out and out v.

[fake v.¹ (2) + SE out and out, complete, extreme]

to kill, to murder.

1812		Vaux Vocab. of the Flash Lang. in McLachlan (1964) 239: To fake a man out and out is to kill him.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.