Turns out it was really murder (duh), and the murderer is after Cook's last recording. He murders two radio station employees with an axe, and strangles Herb's sister Rosalind, all to get Herb's last recording.
Turns out Herb's last recording recorded his own murder!
Turns out it was Herb's manager Phillips. Herb caught him stealing from his accounts, and made him pay him back or he'd send him to prison. Also, Herb demanded he break his engagement to Rosalind.
Turns out the Hangman gets Phillips to confess.