Green’s Dictionary of Slang

murder one n.

[US legal jargon murder one, first degree or premeditated murder]

1. (US drugs) .

(a) heroin and cocaine.

[US]ONDCP Street Terms 15: Murder One — Heroin and cocaine.

(b) a strong variety of heroin.

[US]S. Morgan Homeboy 13: ‘Murder one’ is how Joe Speaker pitched his merchandise.

2. (US black) in pl., dark glasses [the wearing of dark glasses is equated with a murderous image].

[US]K. Scott Monster (1994) 43: I’d [...] put on my murder-ones (dark shades, also called Locs or Locos).
J. Agin Welcome to A Semester in Florence: The Jamie Agin Experience 🌐 [caption to a photo of a woman wearing sunglasses] OK, so this wasn’t from the trip, but it’s Katie Meadows wearing Murder Ones.

In phrases

murder one dun [ety. unknown]

a general greeting.

[US]Hip-Hop Connection Aug. 20: When greeting a friend with the words ‘Murder one dun’, you might not be in the least bit aware what the words coming out of your mouth mean.