LOS ANGELES — Lawyers for Michael Jackson's doctor Conrad Murray faced an uphill battle Monday, launching their case after four weeks of testimony heavily implicating him over the singer's 2009 death.

The last witness for the prosecution said it was a "crazy scenario" to suggest that Jackson could have injected himself with more of the powerful sedative propofol while Murray was out of the room.

The defense is expected to call some 15 witnesses, including medical experts, character witnesses and police, to rebut the charge against Murray, but reports suggest the case could go to the jury by the end of the week.

The first two defense witnesses gave their testimony in less than an hour Monday, after the prosecution rested its case mid-morning.

So far witnesses called by prosecutors have given a litany of evidence suggesting Murray was grossly negligent by administering a deadly cocktail of drugs to help the King of Pop sleep, and abandoning him at the vital moment.

The Trinidad-born medic, who has sat grim-faced throughout proceedings, faces four years in jail if found guilty by a seven-man, five-woman jury at the long-awaited trial.

Jackson died of "acute propofol intoxication" on June 25, 2009 after Murray spent the night unsuccessfully trying to get him to sleep at the star's rented mansion in the plush Holmby Hills district of Los Angeles.

Prosecutors claim Murray, 58, gave Jackson an overdose of propofol -- a clinical anesthetic which he was using as a sedative to treat Jackson's insomnia -- and abandoned his patient at the crucial moment.

Defense lawyers have claimed that Jackson, desperate to get to sleep to be ready for rehearsals for a planned series of comeback concerts in London, could have administered the drug himself.

But in a seeming admission that defense lawyers were struggling, they said on October 12 that they would no longer claim that Jackson could have drunk propofol while Murray was out of the room.

That leaves open the possibility that Jackson self-injected it through his leg IV -- but that was described as a "crazy scenario" by the prosecution's last witness, anesthesiologist Steven Shafer.

The forensic toxicology report two years ago found the cause of death to be acute intoxication of propofol, but also noted the anti-anxiety drug lorazepam was in the singer's system.

Another theory mooted by the defense is that a fatal cocktail was produced when Jackson administered himself some extra lorazepam.

The first witness called by the defense Monday was Dona Norris from the Beverly Hills police department, who began by answering questions about the 911 call placed at 12:20 pm on the day of Jackson's death.

The court also saw grainy black and white footage from security cameras outside the Jackson mansion, as an LA Police Department surveillance expert was questioned before lunch.

The footage showed a convoy of vehicles bringing Jackson home at around 1:00 am on the day of his death, after his latest rehearsal for the ill-fated "This Is It" series of concerts at London's O2 Arena.

One of the highlights at the five-week trial, which started on September 27, was a recording of an interview Murray gave police two days after Jackson's death.

In it the doctor recounted how he battled to help Jackson to sleep, from around 1:00 am, with a series of IV infusions of sedatives before finally agreeing to give him 25 mg of propofol at 10:40 am.

He said he was only out of the room for two minutes to go to the bathroom, and returned to find Jackson not breathing.

But the timeline given was almost immediately called into question by witnesses, including a series of lady friends with whom Murray had telephone calls during a crucial 47-minute period.

Cocktail waitress Sade Anding told how she heard "coughing" and realized Murray had dropped the phone a few minutes before midday -- more than 20 minutes before the 911 call was made.