Law enforcement officials are reportedly calling the death of former "That ’70s Show" star Lisa Robin Kelly a "mystery," TMZ.com reports.

"There were no drugs or alcohol in her room, no vomit in her airway, and no obvious sign of trauma," the story reports, noting that the coroner is performing an autopsy.

As previously reported, Kelly, 43, died in her sleep Wednesday night at a rehab facility where she had voluntarily checked in to a treatment program. The actress had struggled with alcohol-related problems and had a number of DUI arrests and allegations of spousal abuse.

TMZ says Kelly "was not taking any withdrawal drugs at the time she died — at least that’s what the rehab facility told law enforcement … TMZ has learned."

The report adds: "Our law enforcement sources tell us … reps from the L.A. County Coroner and L.A. County Sheriff’s homicide came to Pax Rehab House in Altadena, CA Thursday afternoon, and officials from Pax said unequivocally … they did NOT give Lisa any drugs."

The report notes that Kelly’s boyfriend took her to the hospital Sunday, "where she registered a .34 blood alcohol level, which is borderline fatal. Lisa was admitted to Pax the next day, and she had been to rehab dozens of times before — yes, dozens."