(CBS/AP) LOS ANGELES - On Friday, the attorneys for Michael Jackson's physician will finally get a chance to question the expertise and assumptions laid out by Dr. Steven Shafer, the prosecution's final - and one of its most important - witnesses in the involuntary manslaughter trial of Dr. Conrad Murray.
Defense attorney Ed Chernoff will begin his cross-examination of Shafer, a leading expert in the anesthetic propofol, Friday afternoon.
After days of testimony and demonstrating the type of IV drip that was likely present in Jackson's bedroom in his final hours, Shafer bluntly responded to a question about Murray's culpability.
"He has been entrusted by Michael Jackson to look after his safety every night and he has failed," Shafer said.
Shafer also attempted to discredit the defense theory that Jackson may have swallowed eight lorazepam pills in the hours before his death without Murray's knowledge and that authorities overlooked it. He said the amount of lorazepam that was found in Jackson's stomach was "trivial."
The only explanation that supported all the evidence - including the items found in Jackson's bedroom, the singer's autopsy results and Murray's lengthy statement to police - is that Murray gave the singer propofol on an IV drip and left the room when he thought the singer was safely asleep, Shafer contends.
"This fits all of the data in this case and I am not aware of a single piece of data that is inconsistent with this explanation," Shafer said.
Using charts and his own experience, Shafer said that Jackson likely stopped breathing because of the propofol and without someone to clear his airway. The whole time, propofol would have kept dripping into the IV tube, gravity carrying it into the singer's body.
In all, Shafer said Murray committed 17 violations of the standard of care that could have led to Jackson's serious injury or death.
Murray has pleaded not guilty.