"I can still prove I didn't kill Michael Jackson" - Dr Conrad Murray

Dr. Conrad Murray believes he can still PROVE Michael Jackson injected himself with a fatal dose of Propofol -- and now he's begging an appeals court to let him test his theory.

Murray's lawyers are filing a new motion in his appeal -- claiming a vial of Propofol could hold the key to his innocence ... if only a judge would allow forensic testing to search for traces of lidocaine.

The lidocaine is important because the prosecution argued that Murray hooked MJ up to an IV bag containing the fatal dose of propofol and left him alone ... but first, mixed the Propofol with lidocaine to ease the sting of the drug.

Murray claims testing will prove there was NO lidocaine on the vial ... because Jackson injected himself with a pure dose of Propofol ... and killed himself.

Murray -- who was found guilty of manslaughter and is currently serving time in L.A. County Jail -- has already made two requests for testing. Both were denied by the judge who presided over his trial ... and ruled that Murray should have made the request BEFORE the trial began.

Murray's team will file the motion in California later today. It could take months before the court makes its decision.