The death of a Las Vegas woman who died after receiving a buttocks enhancement injection in a makeshift medical office was accidental, according to an autopsy.

Clark County Coroner P. Michael Murphy told The Associated Press Thursday that 42-year-old Elena Caro died from an adverse drug reaction. He said the autopsy does not preclude criminal charges.

Ruben Matallana-Galvas, 55, and Carmen Torres-Sanchez, 47, face charges of murder and practicing medicine without a license in Caro's April death. Authorities allege the Colombian husband and wife were running a cosmetic surgery business in the back room of a tile store when they injected Caro's buttocks with a gel substance.

Caro was found roaming the streets in agony hours after the injection. She was taken to a hospital, where she died.

Matallana-Galvas and Torres-Sanchez have pleaded not guilty in the case. The husband and wife had hoped to return to their native Colombia before they were arrested, and their lawyers have said the two remain eager to go home.

Police arrested the pair at McCarran International Airport on April 9, hours after Caro's death. The husband and wife had purchased plane tickets to return to their native Colombia on April 22 but were trying to catch an earlier flight.

Under questioning, Matallana-Galvas told detectives that Caro walked away from his office after the procedure, according to a police report.

Caro was married and had a teenage daughter. A week before her death, she had received facial Botox injections from Matallana-Galvas. When no problems arose, she returned for the buttocks injection.

Botox and similar types of injections are minimally invasive but are still considered cosmetic surgery, according to the American Society of Plastic Surgeons.