AceShowbiz -

Autopsy is being carried out to determine the cause of death of "That's '70s Show" star Lisa Robin Kelly, who passed away in her sleep on Wednesday night, August 14. The actress, however, reportedly took no drugs and had no signs of abuse on her body.

Officers of L.A. County Coroner and L.A. County Sheriff's homicide are said to have visited Pax Rehab House in Altadena to seek information concerning the actress' death. Staff members of the rehab facility told the officials that they gave no drugs to the actress before her passing. Law enforcement officers reportedly called the case "a mystery" because they did not see apparent trauma signs on her body and there was no vomit in her airway. They also did not find liquors and drugs in her room.

Kelly's agent Craig Wyckoff previously said that the actress sounded positive and she was looking forward to having new life after rehab. "Lisa had voluntarily checked herself into a treatment facility early this week where she was battling the addiction problems that have plagued her these past few years. I spoke to her on Monday and she was hopeful and confident, looking forward to putting this part of her life behind her," Wyckoff said, adding that cause of death had not been released yet.

Fellow stars on the popular show mourned her death. "Terrible, awful news. Brilliant on 70s.... See u next time LRK, kisses," Danny Masterson, who played Steven Hyde, wrote. Kurtwood Smith, who took part on the show as Red Forman, said in a statement, "I know the last 10 years have been such a difficult struggle for her but I will always remember the lovely, funny and very talented young lady I worked with."

Actress Mackenzie Phillips who previously battled her own drug addiction also paid tribute to the actress. "Rest in Peace Lisa Robin Kelly. #sososad I didn't know Lisa, but in a way, she is me. And I am her. #ThereIsaSolution," she tweeted.