The source initially said Dr. Conrad Murray could be arrested as soon as next Wednesday — but investigators have decided to execute one more search warrant, likely at a Los Angeles pharmacy, next week in an attempt to gather more evidence against him. The arrest is now expected the following week.

Investigators initially had hoped to charge Murray with a more serious crime than manslaughter — a defendant may be charged with second degree murder in California without the presence of a motive — but prosecutors are concerned that a jury will be unlikely to convict without one, sources said. Unless a "smoking gun" is found in next week’s search, Murray will be charged with manslaughter.

Law enforcement sources previously told FOXNews.com that Murray admitted he gave the King of Pop the intravenous anesthetic propofol to help him sleep just hours before his death — and that propofol was at least a contributing factor in the 50-year-old entertainer's death.