A lawyer for Deutsche Bank honcho Brian Mulligan is demanding the LAPD launch a full-blown investigation into the leaked audio tape -- in which Brian admits to using narcotic "bath salts" -- claiming the "leak" was a cheap ploy to smear his good name.
TMZ obtained three letters from Mulligan's new lawyer, Skip Miller -- addressed to the L.A. City Attorney, the Glendale Chief of Police and the L.A. Chief of Police.
The letters state ... the audio -- released earlier this week -- was sent to the LAPD for investigative purposes only (regarding Brian's police brutality claims) and should NOT have been released to the media.
As TMZ previously reported ... Brian filed a $50 mil claim against the City of L.A., alleging two police officers beat the crap out of him on May 15 -- resulting in 15 fractures to his nasal area, a broken scapula, and facial lacerations.
LAPD claims the cops took action ONLY after they perceived him to be a threat.
In the letters, Brian's attorneystates the tape was purposely leaked "out of context" to create a smear campaign against Brian and discredit his accusations against the boys in blue -- all in order to sway the public into believing he "had it coming to him."
Brian's attorney is demanding the LAPD take action stat -- and investigate how the tape got leaked from their department, and explain whether or not it was even legal.
FYI -- The released audio tape was recorded May 13 -- two days before Brian's alleged beat down.
In the audio Brian appears to be acting paranoid ... believes helicopters are following him ... and then admits to a Glendale officer that he has previously used a hallucinogenic narcotic called "bath salts" over 20 times.