TYLER, Texas (AP) — Hospitals operated by a Dallas businessman improperly billed Medicare 80 percent of the time and continued the fraudulent billing even after being warned by government auditors, prosecutors contend in federal court records.

Details of the prosecution’s case against Dr. Tariq Mahmood were disclosed in the recent court filings. Mahmood’s trial on charges of fraud conspiracy began Friday with jury selection and will continue this week in Tyler.