WACO: A US soldier accused of plotting an attack on a military base after fleeing his post as a Muslim conscientious objector went on trial Tuesday wearing a surgical mask and manacled to the floor.

Courtroom security agents behind him wore protective goggles, an apparent reaction to an incident in which the soldier, Naser Jason Abdo, who claims to be HIV positive, bit his lip and spat blood at law enforcement officers.

Prosecutors called the first of 43 witnesses to the stand in a bid to show that Abdo, who fled his post in Kentucky, was gathering bomb-making materials and weapons to attack soldiers and their families at the Fort Hood base in Texas, the cite of a deadly shooting rampage in 2009.

One witness said Abdo told him that the assault was intended to show support for Army Major Nidal Malik Hasan, a Muslim psychiatrist accused of gunning down dozens of people in the 2009 shooting.

FBI agent Charles Owens said that Abdo told him in an interrogation session that “he wanted to do it for the sake of the men and women of Afghanistan, that they had been wronged.”

Abdo was arrested July 27 at a discount hotel in the nearby Texas town of Killeen. Police and federal agents have previously testified that they found a handgun and enough gunpowder to make at least one bomb.

They also discovered directions from an al Qaeda magazine on how to build an explosive device.