Michael Jackson received the fatal dose of Propofol through an IV in his leg, and law enforcement believes Dr. Conrad Murray may have tried covering it up ... this according to law enforcement sources and an anesthesiologist who reviewed the case for the LAPD.

r. Murray told cops he administered only a very small amount of Propofol -- 2.5ml shortly before Jackson died. But Dr. John Dombrowski, a noted anesthesiologist and member of the board of the American Society of Anesthesiologists who reviewed the LAPD file for detectives, tells TMZ that 2.5ml couldn't put Jackson to sleep, much less kill him. Indeed, the Coroner's report notes the level of Propofol found in Jackson's body was equivalent to that found during "general anesthesia for major surgery."

A small, empty, 20ml bottle of Propofol was found in the bedroom, but there was a secret compartment in a nearby closet that could be the key to the prosecution's case. Several days after Jackson's death, law enforcement found numerous bottles of Propofol in that closet, including a large, empty, 100ml bottle with a large tear in the rubber stopper.

The tear could be critical evidence. There are two ways of administering Propofol. The first is sticking a syringe into the rubber stopper, withdrawing a small amount and then injecting it into the tubing. The second way is by using a spike -- which creates a tear in the rubber stop -- and connects the entire bottle of Propofol to the tube.

Dr. Dombrowski says if a spike is used to connect the bottle directly to the IV tube, the doctor must use an infusion pump to regulate the flow of Propofol -- otherwise, the patient could easily OD. There was no infusion pump found in Jackson's home.

Dr. Dombrowski and law enforcement sources believe Dr. Murray may have connected the 100ml bottle of Propofol to the tube, and then either tried regulating the flow by eyeballing it or just letting it flow by itself ... and Dr. Dombrowski calls either scenario "reckless." Remember, Dr. Murray himself told detectives at one point he walked out of Jackson's room to go to the bathroom.

If Dr. Murray did indeed attach the 100ml bottle to the tube and the contents emptied into Jackson's system, that would be 40 times more Propofol than Dr. Murray said he administered.

There is no explanation for the empty bottle of Propofol in the hidden compartment.

Source: tmz.com