The Justice Department has opened a criminal investigation in California as it continues its effort to prove that as many as 20,000 noncitizens are on the state’s voter rolls, a U.S. official confirmed to NBC News on Thursday.

The official said the Justice Department has issued federal grand jury subpoenas to local election officials across the state. It’s unclear how many subpoenas were sent out and exactly who received them.

The New York Times first reported the new subpoenas.

In response to an inquiry from NBC News on Thursday, the Justice Department declined to comment on “leaks about alleged grand jury subpoenas” but said federal courts have said voting unlawfully results in criminal exposure.

The U.S. official told NBC News that receiving a subpoena doesn’t mean a person is necessarily a target, just that the person may have information relevant to the investigation.…