Murder one usually refers to first-degree murder.

Murder One may also refer to:

Film and TV
Murder One (film), a 1988 biographical crime drama film
Murder One (TV series), American legal serial broadcast on ABC in 1995–96
Murder 1 (film), first installment, in 2004, of Bollywood film series, Murder

Music 
 Murder One, album by Paul Di'Anno
 Murder One, former band of a member of Mob Rules
 Murder One, bass amplifier head blown up by Lemmy
 Murder One Records, label for Sean T

Songs 
 "Murder One", song by 50 Cent from The Lost Tape
 "Murder One", song by Metallica from Hardwired... to Self-Destruct
 "Murder One", song by Sodom from In War and Pieces

Other
Murder One (bookshop), book store in London, open from 1988 to 2009
Heroin (slang)