Police are investigating the death of a 28-year-old Alton woman as a possible overdose of the synthetic drug commonly known as bath salt, according to the Madison County Coroner’s Office.

Tonia Whitehead, of 417 Brookside Ave., was pronounced dead at 10:16 a.m. Wednesday at Alton Memorial Hospital, according to Coroner Steve Nonn and the office’s Chief Investigator Roger Smith.

An autopsy was being conducted Wednesday on Whitehead’s body.

An official cause of death will not be determined until the results of toxicology tests are released in six to eight weeks, Nonn said. This would be the first bath salt overdose death in the county, he said.

The woman was found unresponsive at approximately 10 a.m. Tuesday inside her residence, according to Alton Police. She was taken to the hospital where she remained in critical condition until her death.

Whitehead had ingested bath salt that was purchased from an unidentified Alton liquor store. Detective obtained a search warrant Tuesday afternoon and searched the store, recovering evidence of substantial amounts of bath salts and financial records associated with the sale of the substance.

Detectives also found video gaming devices inside an illegal back room gambling operation at the store.

A store employee and an acquaintance of the victim have been taken into custody pending criminal charges. The investigation is now focused on who was responsible for the sales, transfer or facilitation of the substance that caused the victim’s death.