Michael Jackson's death is being investigated by the Drug Enforcement Administration (DEA).
The DEA - which looks at cases involving prescription drug use - is helping the Los Angeles Police Department (LAPD) with their ongoing inquiry into the pop singer's death.
A statement issued by the DEA said: "We routinely offer assistance to any agency regarding the Federal Controlled Substance act, however at this time we have nothing further to comment about the death of Michael Jackson."
Unnamed prescription medications have reportedly been taken from Michael's Los Angeles home following his death from a suspected cardiac arrest last Thursday (25.06.09).
It has been claimed the singer was taking up to seven different prescription medications, possibly including Propofol, a sedative so strong it is used to put people to sleep before surgery.
The LAPD is said to be attempting to speak to several doctors believed to have written prescriptions for the late King of Pop, which the DEA is helping them with.
It is claimed Michael used several aliases to gain various prescriptions, including Omar Arnold and Jack London.
Gossip website TMZ reports: "Jackson also used the name of one of his bodyguards, as well as the name of the office manager for one of his doctors.
"The DEA, which is joining to assist the LAPD in its investigation of several doctors who prescribed drugs to Jackson, will be hunting down these names and others."
Police have reportedly impounded a car from outside Michael's Holmby Hills home as part of the case, although it is unknown who it belonged to.
Last week, police seized a vehicle belonging to Michael's personal physician Dr. Conrad Murray - who was with him when he died and administered CPR - from outside the star's property.
Michael's unofficial biographer Ian Halperin is set to release a new book called 'Unmasked: The Final Years of Michael Jackson' about the pop star.
The tome will examine the singer's alleged use of prescription drugs and links to Scientology.
Vice president and publisher of Simon Spotlight Entertainment, Jennifer Bergstrom, said: "If you think you know everything there is to know about Michael Jackson you're wrong. Ian has uncovered startling new information that will make this book the definitive biography of the most iconic performer of our time."
Meanwhile, Grace Rwaramba - the nanny who looked after Michael's three children, Prince Michael, 12, Paris, 11, and seven-year-old Prince Michael II - has denied reports she used to pump the singer's stomach, claiming she never gave the interview which has been widely reported.
She said in a statement: "I am shocked, hurt and deeply saddened by recent statements the press has attributed to me, in particular, the outrageous and patently false claim that I 'routinely pumped his stomach after he had ingested a dangerous combination of drugs'. I don't even know how to pump a stomach!!
"The statements attributed to me confirm the worst in human tendencies to sensationalise tragedy and smear reputations for profit."