Lies, weak regulation and poor communication allowed a radiology technician to move from job to job around the U.S. , even after he was fired twice by hospitals that said they caught him stealing drugs or tampering with medications.

David Kwiatkowski was arrested in July and charged in New Hampshire with tampering with needles and infecting at least 31 people with hepatitis C, a potentially life-threatening virus. Thousands more people treated at hospitals where he worked are being tested.

Records and interviews conducted by The Associated Press show that authorities could have halted Kwiatkowski’s career four years ago, after he was fired from a Pittsburgh hospital. But he went on to work at 10 more hospitals, none of which knew about his history.

Two patients that were treated at Hays Medical Center during Kwiatkowski’s time there, were informed that they tested positive for Hepatitis C, last week.

Kwiatkowski has pleaded not guilty.