"While Chicago is 1, 500 miles from Mexico, the Sinaloa drug cartel is so deeply embedded in the city that local and federal law enforcement are forced to operate as if they are on the border, " said Jack Riley, who heads the Drug Enforcement Administration's office in the city.

CNN: Chicago's new Public Enemy No. 1: 'El Chapo'

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