WASHINGTON (AP) — A person familiar with an investigation into potential coordination between Russia and the Trump campaign says Special Counsel Robert Mueller is using a grand jury in Washington as part of the probe.

The person was not authorized to discuss the ongoing investigation by name and spoke on condition of anonymity. The Wall Street Journal first reported the grand jury.

Mueller was appointed special counsel in May following the firing of FBI Director James Comey.

Meanwhile, lawyers for Trump say they have no reason to believe the president himself is under investigation.

Grand juries are common vehicles to subpoena witnesses and records, though they do not suggest any criminal charges are near. A grand jury in Virginia has been used to gather information on Michael Flynn, Trump’s former national security adviser.