(KRON) — A Santa Rosa doctor was sentenced to 30 months in prison for prescribing certain drugs to clients without a legitimate medical need, the United States Department of Justice (DOJ) said. Thomas Keller, 75, was found guilty of distributing drugs including oxycodone to a 17-year-old girl who later fatally overdosed.

The patient in question was dealing with mental health issues when she came to Keller’s pain management practice, per the DOJ. On Dec. 22, 2016, Keller prescribed her “high dosage levels” of Oxycodone, Carisoprodol (also known as Soma), and Diazepam (also known as Valium) to her. Trial evidence suggests the girl’s mental condition made these drugs more dangerous.

“At trial, the evidence demonstrated that Keller repeatedly prescribed the opioid oxycodone and other strong, addictive drugs to his patient in dosages and combinations that far exceeded the usual course of professional practice and were for no legitimate medical need,” the DOJ said.

On Jan. 20, 2017, Keller gave more Valium to the victim. On Feb. 16, he gave her Oxycodone despite knowing that the drugs did not serve a “legitimate medical purpose,” per the DOJ. He prescribed more Soma on July 10. About two weeks later, the girl died from an overdose on Oxycodone and other drugs.

“Trial evidence established that the combination of an opioid, a benzodiazepine, and Soma together – colloquially known as “the Holy Trinity” – is an extremely dangerous combination of drugs; nevertheless, Keller prescribed this combination of drugs to (the victim) repeatedly for more than two years,” the DOJ said.

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In court, the government stated that Keller prescribed the drugs despite knowing the addictiveness of the substances. His journal entries were used as evidence.

Keller was indicted on Sept. 27, 2018, and convicted of four counts of unlawful distribution of controlled substance on Nov. 3, 2022. In addition to serving prison time, he will have a three-year term of supervised release.