LOS ANGELES (AP) — For several moments, the milky white substance that authorities say killed Michael Jackson dripped down into an IV line a few feet away from jurors.

Sometimes the drops fell fast, until their rate was slowed by the Columbia University researcher and professor who for three days has testified about the drug and its effects on the King of Pop as he died. The demonstration, with the anesthetic propofol dripping harmlessly into a water bottle, was one of the final scenes prosecutors presented Thursday to jurors hearing the involuntary manslaughter trial of Dr. Conrad Murray.

On Friday, Murray’s lead attorney will finally get his chance to question the expertise and assumptions laid out by Dr. Steven Shafer, the prosecution’s final and one of its most important witnesses. The Houston-based cardiologist has pleaded not guilty.

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.

Sitting in the courtroom, watching and listening to it all was Shafer’s former teacher and longtime colleague, Dr. Paul White, who will testify for the defense.