By beating the balloon game at Whysoserious.com/Redballoons, Whysoserious.com/Redballoons/Ineptlackeys.htm was discovered. The page contains a note from the Joker:
Hired goons are so unreliable these days. That's why I only employ the ones that graduated from the top of their class at Clown College (and being opera-lovers didn't hurt, either). But Maroni's got his hands full with inept lackeys like little Stevie and Romeo, Romeo, wherefore art thou, Romeo? I'll tell you where they are: sittin' pretty with a smile on their face. They tried to reschedule their pick up service at Pasquale's, but things didn't go according to plan.
Since the note mentions opera and Pasquale's Bistro it was found that "verdi" (as in renowned opera composer Giuseppe Verdi) was the passcode for the bistro's voicemail.
(Whysoserious.com/Redballoons/Ineptlackeys.htm) -- direct link