Robert Durst Also May Face Federal Gun Charge After Louisiana Gun, Drug Indictments

— -- Already awaiting a scheduled arraignment Thursday on state gun and drug possession charges stemming from his arrest in New Orleans, Robert Durst now may face a federal weapons charge, as well, according to an FBI affidavit.

The affidavit, part of a federal criminal complaint filed in U.S. District Court in New Orleans on Tuesday and just released, cites Durst's 2004 federal firearm conviction and says probable cause exists for Durst to face the new federal charge of possession of a firearm by a felon.

Durst is expected to attend his arraignment on the Louisiana state charges Thursday at 10:30 a.m. ET in New Orleans, according to a court administrator. Prosecutors said today that a grand jury has indicted Durst on the charges.

The details about the scope of the grand jury remain unknown but the New Orleans District Attorney's office confirmed the indictment to ABC News this morning. The indictment is in connection with his March 14 arrest on charges of illegal possession of a firearm by a felon and illegal possession of a firearm in the presence of a controlled substance.

The real estate heir was charged with the unsolved 2000 murder of his friend Susan Berman in California, but when police arrested him in a New Orleans hotel last month, they filed additional charges against him because he was allegedly found to have a gun and marijuana with him.

Now, he may face the federal weapon charge in Louisiana over the same alleged gun discovery. It was not clear when or if Durst will appear on the federal weapon charge.

In response to word of the possible federal case, Durst's attorney, Dick DeGuerin, said, "Now everyone is just piling on." He added that he did not yet know how the federal and state authorities would balance out their cases.

DeGuerin has been fighting to have Durst extradited to California so he can face the murder charge. Though he has not yet had to enter a plea in the California case, DeGuerin has said publicly that Durst did not murder Berman. Durst has not yet made a plea in the Louisiana case and his lawyer has not commented on the substance of the charges.

The circumstances around the search that resulted in the gun and drug charges have also come under scrutiny as DeGuerin argued in a previous court hearing that they were done illegally, though no formal ruling has been announced on that topic.

The millionaire who was the focus of an HBO docuseries "The Jinx" is being held without bond at a jail in St. Gabriel, Louisiana, pending possible extradition to face the California charges.

ABC News' Seni Tienabeso and Michel Brewer contributed to this report.