But Stack has been slapped with two civil suits in what police called the largest prescription-drug case in Utah history.

Tyler Lugo, 24, died of prescription drug toxicity on April 9, nine months after he began seeing Stack, according to a wrongful death suit filed by Lugo's parents in 3rd District Court.

Ryan Call, 26, overdosed four times between December and March, as Stack prescribed larger and larger doses of pain medication, according to Call's medical malpractice lawsuit in the same court.

Police began looking into Stack's practice after receiving information from informants that he was a well-known source of prescription painkillers. Undercover officers followed up by personally obtaining prescriptions from Stack.

Stack was allegedly distributing Oxycontin, oxycodone, Xanax, methadone and hydrocodone, police said. A large portion of the drugs were being sold by the patients throughout the Salt Lake Valley, police said.

When police arrived May 16 to arrest Stack, his waiting room was crammed with people, and more were standing outside. But the waiting room quickly emptied, and several cars pulling up to the doctor's office building made U-turns and drove off, apparently after seeing sheriff's vehicles.

Stack bailed out of jail the day after his arrest and surrendered his license to practice medicine in July, according to David Stanley, director of the Utah Division of Professional Licensing (DOPL).

The U.S. Attorney's Office is investigating, but spokeswoman Melodie Rydalch would not comment on whether charges might be filed.

The lengthy initial investigation was conducted jointly by DOPL, the federal Drug Enforcement Agency and the Salt Lake County Sheriff's Office.

shunt@sltrib.com