Authorities remain suspicious of the cause of Lisa Robin Kelly's death - the former star of That 70s Show found dead at a rehab facility last week.

Law enforcement sources tell TMZ.com that both the L.A. County Coroner and the L.A. County Sheriff are conducting separate investigations after discrepancies over the death arose.

A doctor at the rehab facility pronounced Kelly dead at 08.07am on Thursday (August 15, 2013) though the coroner didn't find out until noon, when an official from his office saw a post online.

The rehab doctor told the coroner that the actress died from an embolism - a blood clot - though the coroner scoffed at the conclusion because there's no way of knowing that someone died from an embolism without performing an autopsy, which is pretty obvious.

Insiders say the doctor at the facility told the coroner that Kelly was taking detox drugs, though the toxicology report isn't in yet, so it's unclear if the drugs played a part in her death. The authorities are suspicious are the whole thing, and the Sheriff has issued a security hold on the case, meaning no information can be released while the death is being investigated.

Lisa Robin Kelly had struggled with personal problems in recent years, including a drug addiction. 

A funny and talented actress in her day, Kelly is best known for playing Laurie, the promiscuous older sister of Eric Foreman on That 70s Show. She was known for dating Ashton Kutcher's character, under the watchful eye of her father, Red.

After five years, she was written out of the show.

In an interview with ABC News she admitted that "With That '70s Show I was guilty of a drinking problem, and I ran to attend beauty school."

Lisa Robin KellyLisa Robin Kelly Died Last Week