Following Jackson's death, allegations emerged that the 50-year-old King of Pop had been consuming painkillers, sedatives and antidepressants.
The DEA was asked to help the probe by the Los Angeles Police Department, a law enforcement official in Washington told The Associated Press on condition of anonymity because of the sensitivity of the investigation.
The federal agency can provide resources and experience in investigating drug abuse, illicit drug manufacturers known as "pill mills" and substances local police may not be familiar with, the official said Wednesday.
While the investigation into the singer's death deepened, passionate Michael Jackson fans spent another day in an uneasy limbo, awaiting word from the King of Pop's camp about where and when a memorial service might be held for their hero — and if they're even invited.
Speculation about the potential location of a memorial ricocheted during the day from the Staples Center to the Los Angeles Coliseum to the Nokia Theater.
One spot that was ruled out as an immediate memorial venue was Jackson's sprawling Neverland ranch in Santa Barbara County. Jackson family spokesman Ken Sunshine said a public memorial was in the works for Jackson but it wouldn't be held at Neverland.
That came as a blow to many Jackson fans who had already descended on the estate in the rolling hills near Santa Barbara with the hope of attending a public viewing.
"We're terribly disappointed," said Ida Barron, 44, who arrived with her husband Paul Barron, 56, intending to spend several days in a tent.
It appeared more likely that a funeral and burial would take place in Los Angeles, a person familiar with the situation told The Associated Press.
Many of Jackson's die-hard fans refused to believe that the family would bury their most famous son without acknowledging the supporters who helped propel him to superstardom.
"I can't believe they wouldn't do something for his fans," said Rosie Padron, who had roped off a spot just outside the Neverland gates. "Michael loved his fans."
New Yorkers weren't willing to wait. The weekly Amateur Night at the Apollo Theater turned into a Jackson celebration, with impersonators emulating his outfits and mimicking his dance moves.
Allison Hector, who wore a T-shirt with the image of the "Thriller" album cover, ecstatically emulated moves she learned watching Jackson's music videos.
"Nobody moves like him," the 19-year-old said, her eyes filling with tears. "I feel it in my blood — I just can't help it!"
On the legal front, Jackson's 7-year-old will was filed Wednesday in a Los Angeles court, giving his entire estate to a family trust and naming his 79-year-old mother Katherine and his three children as beneficiaries. The will also estimates the current value of his estate at more than $500 million.
Katherine Jackson was appointed the children's guardian, with entertainer Diana Ross, a longtime friend of Michael Jackson, named successor guardian if something happens to his mother. A court will ultimately decide who the children's legal guardian will be.
Jackson's lawyer John Branca and family friend John McClain, a music executive, were named in the will as co-executors of his estate. In a statement, they said the most important element of the will was Jackson's steadfast desire that his mother become the legal guardian for his children.
"As we work to carry out Michael's instructions to safeguard both the future of his children as well as the remarkable legacy he left us as an artist, we ask that all matters involving his estate be handled with the dignity and the respect that Michael and his family deserve," the statement said.
The will doesn't name father Joe Jackson to any position of authority in administering the estate. Also shut out is ex-wife Debbie Rowe, the mother of his two oldest children.
The executors moved quickly to take control of all of Michael Jackson's property, going to court hours after filing the will to challenge a previous ruling that gave Katherine Jackson control of 2,000 items from Neverland.
Paul Gordon Hoffman, an attorney for the executors, told Superior Court Judge Mitchell Beckloff his clients are the proper people to take over Jackson's financial affairs. He called Katherine Jackson's speed in getting limited power over her son's property "a race to the courthouse that is, frankly, improper."
Judge Beckloff urged attorneys from both sides to try to reach a compromise. A hearing on the estate was set for Monday.
The will, dated July 7, 2002, gives the entire estate to the Michael Jackson Family Trust. Details of the trust will not be made public.
Jackson owns a 50 percent stake in the massive Sony-ATV Music Publishing Catalog, which includes music by the Beatles, Bob Dylan, Neil Diamond, Lady Gaga and the Jonas Brothers.
Jackson, who died June 25 at age 50, left behind three children: son Michael Joseph Jr., known as Prince Michael, 12; daughter Paris Michael Katherine, 11; and son Prince Michael II, 7. Rowe was the mother of the two oldest children; the youngest was born to a surrogate mother, who has never been identified.
Rowe, who was married to Jackson in 1996 and filed for divorce three years later, surrendered her parental rights. An appeals court later found that was done in error, and Rowe and Jackson entered an out-of-court settlement in 2006.
Neither Rowe nor her attorneys have indicated whether she intends to seek custody of the two oldest children.
AP writers Michael R. Blood, Noaki Schwartz and Ryan Nakashima in Los Angeles; John Rogers in Los Olivos; Michele Salcedo in Washington; and AP Entertainment Writer Erin Carlson in New York contributed to this story. From Yahoo News