An attorney for Michael Jackson's in-house doctor challenged a crime scene investigator on Thursday and suggested she conducted a shoddy examination of the bedroom where the Thriller singer stopped breathing in 2009.

The testimony of coroner's investigator Elissa Fleak came midway through prosecutors' presentation of their case in the involuntary manslaughter trial of Dr. Conrad Murray.

Murray's attorney, Ed Chernoff, mounted the defense team's most forceful challenge since the trial began in Los Angeles on September 27.

Murray has admitted to giving Jackson the powerful anesthetic propofol, through an intravenous infusion, as a sleep aid on June 25, 2009. His attorneys claim Jackson gave himself an extra, fatal dose of the drug once Murray was out of the room.

Fleak combed through Jackson's bedroom with police after the singer's death.

Would you agree with me that you made a substantial number of mistakes in your investigation? Chernoff asked her.

Fleak denied that suggestion, but acknowledged that her original hand-written notes were destroyed when they were transferred into an official report. I do that in all my cases, she added.

Chernoff questioned Fleak on her assertion that a bottle of propofol was found inside an IV bag.

Investigators found the propofol bottle and IV bag stashed inside a shopping bag in a closet area four days after Jackson's death, Fleak said.

Prosecutors and defense attorneys agree that Murray's fingerprint was on the propofol bottle.

Fleak admitted that her original notes did not mention finding the propofol bottle inside the IV bag, and that the first time she placed that in her notes was earlier this year.

Security guard Alberto Alvarez, one of the first members of Jackson's staff on the scene after the singer stopped breathing, has testified that he saw a vial of a drug with a milky substance -- which prosecutors say was propofol -- inside an IV bag. Alvarez said he put them in a shopping bag at Murray's urging.

Fleak denied suggestions by Chernoff that she had changed her findings to make them fit Alvarez's story, at the urging of prosecutors. I've never talked to prosecutors about another witness, she said.

Fleak said she photographed the IV bag and the propofol bottle, after taking the bottle out of the bag, to show they were found together.