Former Casper Dr. Shakeel Kahn, on trial for operating a multi-state prescription drug conspiracy, admitted he sometimes kept sloppy records but never prescribed pain medicines for illegal reasons, he told the jury in federal court Friday.

Kahn took the stand in his own defense and emphatically told the jury that he never prescribed controlled substances such as oxycodone and Xanax for his patients to abuse or to sell, nor did he ever accept any money from illegal drug sales, he said on the 15th day of the trial in the case that started three years ago.

Under questioning by defense attorney Michael Thompson, Kahn said he regrettably did not act as diligently as he should have with patients who violated the forms they signed in which they agreed to take their medicines as prescribed and not transfer or sell them to others.

In other words, patients who testified on behalf of the prosecution lied to Kahn to receive the powerful drugs and support their addictions, he said.

"Looking back, there are things I should have done differently," he said at the end of nearly seven hours of testimony.

"I learned about deception and lies," Kahn said.

If he ever practices medicine again -- his medical licenses in Wyoming and Arizona were suspended in 2016 -- he will do more to make his practice safer, cleaner and better to help his patients, he added.

After months of investigations in Arizona and Wyoming by state and federal authorities, Kahn and his wife Lyn were arrested Nov. 30, 2016, and initially charged with one count of conspiracy to sell oxycodone. The number of counts expanded to 23, with Shakeel Kahn charged with 21 of them including conspiracy to distribute oxycodone and other drugs resulting in death, operating a continuing criminal enterprise, having a firearm during a drug trafficking crime, unlawful use of communication device, and money laundering.

If convicted on all counts, he faces at least 45 years imprisonment

His brother Nabeel Khan [sometimes spelled Kahn] also is on trial for conspiracy to distribute oxycodone and other drugs resulting in death, and brandishing a firearm during a drug trafficking crime. If convicted, he faces at least 27 years imprisonment.

Three other defendants in the case -- Kahn's wife Lyn, Shawnna Thacker and Paul Beland -- have pleaded guilty to some of the counts, agreed to testify, and will be sentenced later this summer.

Nabeel Khan's attorney Stephanie Bowen reserved making her opening statement for him in the trial for Friday. Bowen told the jury that Nabeel Kahn is not the central defendant, and it's not about what he did to help his brother in his office in Fort Mohave, Ariz.

None of the evidence presented has shown he wrote prescriptions or was present in in exam rooms with the patients, Bowen said. Nabeel Kahn did like to carry a pistol at work, which is legal in Arizona, she added.

Bowen echoed Thompson's opening statement two weeks ago that the case is not about medical malpractice, but whether the Kahns intended to commit crimes.

During the questioning by Thompson, Shakeel Kahn gave an overview of his life, starting with his birth 53 years ago in Bloomington, Ind., moving to Canada a month later, having a tight-knit family with his brothers Nabeel and Jameel, earning bachelor's and master's degrees, studying at the University of Toronto and then earning his medical degree in Belize, returning to the United States in 2004, meeting Lyn Voss when he was a resident at the Community Health Center of Central Wyoming in 2005, falling in love with her and marrying her in 2015.

He started working at a hospital in Fort Mohave, then created his own company called Medicorp and opened his own family medicine practice there in 2008.

This area in western Arizona was medically underserved. Kahn kept seeing patients who were in pain and not able to fully enjoy life, he said.

He transitioned to specializing in pain management in late 2011, and based on his understanding of treating pain, would aggressively prescribe opioids for patients instead of taking a more gradual approach that he thought was ineffective, he said.

However, that caused problems with pharmacists and others filing complaints such as apparent over-prescribing, Kahn said. The complaints to the Arizona Board of Medicine led to several investigations that cleared him four times of wrongdoing, he said. "It confirmed what I was doing was correct."

Pain is a subjective feeling, and treating it is often a matter of trial and error by relying on patients' medical history, their ability to describe what hurts, and feedback on what the medicines are doing, Kahn said.

He also knew that drugs such as oxycodone can be highly addictive and lead to abuse and illegal activities, so he contacted the U.S. Drug Enforcement Administration to make sure he practiced within the law, he said.

As his practice grew, he learned some hard lessons about patients who tried to deceive him, but also that he had an obligation to treat them.

If he heard a rumor that a patient was selling the drugs, he said he would confront them. But he couldn't dismiss them without proof, otherwise he would be opening himself to lawsuits, he added.

So when a prospective patient came to him, that patient needed to fill out a series of forms starting with biographical information, medical history and records, charts showing where the pain was, and their commitment to take the medicines as prescribed, and not sell or give them to other people -- the latter being federal crimes.

"You have to trust your patients," he said.

One of the forms had a statement in which the patient would swear to never call him a "drug dealer," or else risk court action, he said. That form was the result of an irate patient who yelled "'you're nothing but a drug dealer'" in his office. Nabeel suggested adding the "drug dealer" comment as a result of that incident, Shakeel Kahn said.

He also would vet his patients as much as possible by doing internet research, asking about addiction issues, and searching the Wyoming Prescription Drug Monitoring Program.

Through his experiences with insurance companies, credit and debit cards, and payment by checks, Kahn shifted his business practices to a cash-only basis that may have been unusual but not illegal, he said.

Kahn defended charging patients differently for office visits because those with more prescriptions and higher doses because those patients required more time and care, he said. He never based his rates on the amount or strength of the medicine, he added.

He also would accept goods and services, such as firearms and dental care, in lieu of cash payment for office visits, he said. "The barter system is the oldest form of trading."

Throughout the day, Thompson reviewed the testimonies of the former patients called by the prosecution.

Some of those patients lied when they signed the contracts, something they did on every office visit, Kahn said.

For example, Deni Antelope had been treated before for pain issues and she reported to him a couple people she knew were selling pills at a casino, he said. That she would do that validated his trust in her, he added.

As it turned out, Antelope and her husband Dustin Big Medicine were among 15 central Wyoming residents indicted in Natrona County District Court and later pleaded guilty to drug distribution crimes related to the Kahn case.

In another example, he said he believed former patient Anthony Vargas was using his medicines as prescribed. Sometimes Vargas would come in with his girlfriend Jessica Burch who were both in Arizona, but that was not unusual. Nor was it unusual that one of them would pick up a prescription for the other.

At one time, Vargas was jailed for a non-drug related crime. Burch would pick up his prescriptions and Kahn found out later that those medicines were never received by Vargas and he had no reason to believe that Vargas was not receiving them.

Burch, he added, was his patient for lower back pain for three years, and he had no reason to believe she was using opioids inappropriately by cursing them and injecting them. Burch had seizures and Kahn referred her to a neurologist.

Burch did not tell Kahn she was pregnant, which would have meant a change in the dosage of Xanax, he said. She also was snorting the Xanax, something he never advised, he added.

Burch later died from an overdose.

Kahn said he should have been more attentive to her condition and not have trusted her as much as he did.

Thompson also showed transcripts of phone calls between Kahn and Beland, which the prosecution presented as evidence that Kahn knew he was prescribing drugs illegally.

During those calls, Kahn would often respond with "yeah" or other cursory responses because Beland liked to talk and Kahn just wanted him to end the call, he said. "I was just blowing him off."

Beland pleaded guilty to conspiracy to distributing oxycodone and other drugs, and to unlawful use of a communication device, but Kahn told the court that he had no reason to believe Kahn was selling the drugs illegally.

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The trial resumes at the Ewing Kerr Federal Courthouse, 111 S. Wolcott, at 9 a.m. Monday. The prosecution is expected to conduct an extensive cross-examination.