SAN BERNARDINO The San Bernardino County District Attorney's office has served four county supervisors with subpoenas requesting they testify before a criminal grand jury.

The nature of the investigation tied to the subpoenas was not immediately clear.

First District Supervisor Brad Mitzelfelt, who represents the High Desert, received his subpoena Friday morning, he confirmed by phone. He said he has "no idea whatsoever" about the reason he's being called to testify later this month.

Third District Supervisor Neil Derry received his subpoena around 5 p.m. Thursday and is scheduled to testify as a witness to a special grand jury on April 14, according to George Watson, Derry's chief of staff. Steve Hauer, deputy chief of staff for Derry, was also called as a witness.

Subpoenas have also been issued to 5th District Supervisor Josie Gonzales and 4th District Supervisor Gary Ovitt, according to multiple knowledgeable sources.

Newly elected 2nd District Supervisor Janice Rutherford was reportedly not summoned by the grand jury.

It's the second time that county supervisors have been called before the grand jury in less than two years.

In August 2009 county supervisors and other government officials were issued grand jury subpoenas tied to corruption probes.

When asked about the nature of the grand jury subpoenas issued this week, District Attorney's office spokeswoman Susan Mickey said she could not comment on ongoing investigations.