Washington, March 5 - A federal grand jury Friday issued a 49-count indictment against the gunman accused of killing six people and injuring 13 in an Arizona attack targeting Congresswoman Gabrielle Giffords in January.

Jared Lee Loughner, 22, is charged with the murder of US District Judge John M. Roll and Gabriel M. Zimmerman, an aide to Giffords, according to the new indictment released by the Justice Department.

In a novel legal strategy, Loughner will also face federal charges for causing the death of four participants at a federally provided activity. Previously Loughner had been expected only to face state charges for the attack on non-federal employees.

The college dropout has pleaded not guilty to three previous federal counts related to the deadly attack.

US Attorney Dennis K. Burke said that the indictment involves "potential death penalty charges" and that Loughner would be arraigned next Wednesday in a Tucson courtroom.

Six people were killed and 13 were injured in the attack at a shopping mall in Tucson, Arizona, Jan 8 when Loughner allegedly opened fire as Giffords was meeting constituents.

Giffords was gravely injured in a shot to the head, but survived and is currently undergoing rehabilitation in Houston, Texas. (IANS)