Congressman Gary Condit has been subpoenaed by a D.C. grand jury investigating the disappearance of Chandra Levy.

The Superior Court panel is looking into what happened to the missing 24-year-old intern, law enforcement authorities tell The Washington Post. Sources also say the grand jury also plans to call other witnesses, including Levy's friends and members of Condit's staff.

Levy mysteriously vanished May 1 while making plans to return to California. Officials say investigators still have no clue what happened to her.

Authorities have said Condit isn't a suspect. But they complained that he was less than forthright in some of their meetings with him. Condit admitted that he had an affair with Levy.

Two D.C. police detectives and two FBI agents are still working the case.

Condit's expected to testify early next month.

The Associated Press contributed to this report.