In legal papers filed today and obtained by TMZ ... Dr. Murray challenges Joe Jackson's decision not to name Dr. Klein as one of the physicians allegedly responsible for his son's death.
In the new docs, Murray quotes from Joe's lawsuit, "Dr. Klein may have been medicating Michael Jackson up until or even beyond June 18, 2009, less than one week before Michael Jackson's death."
And Murray continues quoting from Joe's lawsuit that Dr. Klein "prescribed or may have over medicated Michael Jackson including to such point that AEG Live, LLC had to hire Dr. Murray in order to separate Michael Jackson from Arnold Klein."
And Murray goes on to quote Joe's lawsuit which claims "AEG Live, LLC read Michael Jackson the proverbial 'riot act' to get him to stop subjecting himself to overmedication by Dr. Arnold Klein."
So with all that, Dr. Murray concludes, "The plaintiff [Joe Jackson] does not explain why, given these allegations, Dr. Arnold Klein is not a required party to be added to accord proper relief."
In other words ... why didn't Joe sue Arnie?
As TMZ first reported, Dr. Klein shot Michael full of Demerol -- 51 injections in a 3-month span, right up until the week of his death.
Dr. Murray also points the finger at other doctors who treated Michael Jackson, citing TMZ stories revealing that 7 doctors other than Murray were fueling MJ with meds at or near the time of his death.
Murray's team also asked the court to dismiss Joe's wrongful death lawsuit -- claiming Jackson doesn't have the right to file because he's not a beneficiary of MJ's estate.