The panel was convened recently and will sit three days a week for six months. It is likely to hear several matters — not just the Trump case ­— during the duration of its term, which is longer than a traditional New York state grand-jury assignment, these people said.

Like others, they spoke on the condition of anonymity to discuss an ongoing investigation. Generally, special grand juries such as this one are convened to participate in long-term matters rather than to hear evidence of crimes charged routinely.

Shayna Jacobs is a federal courts and law enforcement reporter on the national security team at The Washington Post, where she covers the Southern and Eastern districts of New York.

David A. Fahrenthold is a reporter covering the Trump family and its business interests. He has been at The Washington Post since 2000, and previously covered Congress, the federal bureaucracy, the environment and the D.C. police.