Green’s Dictionary of Slang

slab v.

[i.e. to send to the mortuary/undertaker’s slab]

(Aus. prison/US und.) to murder.

[Aus]Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Slab. To kill.
[US]T. Piccirilli Last Whisper in the Dark 287: Danny had been targeted for something much worse than being slabbed.