SANTA ROSA, Calif. (AP) — A federal jury convicted a 75-year-old California physician of prescribed an opioids and other powerful drugs to a patient who didn’t need them and who eventually died of an overdose, prosecutors said.

While running a pain management clinic in Santa Rosa, Thomas Keller prescribed drugs “in dosages that far exceeded the usual course of professional practice and was for no legitimate medical need,” the U.S. Attorney’s Office said in a statement.

Jurors on Thursday found Keller guilty of four counts of distributing controlled substances outside the scope of his professional practice, prosecutors said.

Keller was indicted in 2018. Evidence at trial showed Keller prescribed oxycodone, diazepam and carisoprodol to a woman who overdosed and died, according to prosecutors.

Keller could face 20 years in prison when he’s sentenced.