Along with the police investigation, which is being aided by the state attorney general's office and the Drug Enforcement Administration, the Los Angeles County coroner's office has also drawn up a list of Jackson's doctors and is trying to talk to them to determine what drugs they may have prescribed him.

CNN: Portrait of Jackson's pill consumption emerges

It is also the focus of an investigation by police, the state attorney general's office and the U.S. Drug Enforcement Administration.

CNN: More associates link Jackson to prescription drugs

It must have been a major disappointment to the FBI's New York field office when, in February 2000, Drug Enforcement Administration (DEA) agents arrested Gravano and others in connection with a massive ecstasy ring in Arizona.

BBC: FBI and the mafia: A tale of betrayal