(CNN)The FBI is conducting an internal review into possible misconduct related to the Trump-Russia investigation, including potentially improper handling of a surveillance warrant that was used early in the investigation, an FBI agent revealed Tuesday in federal court. FBI supervisory agent Curtis Heide testified that an administrative inquiry is underway, and that multiple FBI agents are being scrutinized, including himself. Heide said the inquiry is being handled by the FBI's Inspection Division, which conducts internal audits and can refer any wrongdoing it finds to the Office of Professional Responsibility, which can recommend discipline or even firings.