A U.S. Army veteran with experience fighting in Afghanistan conspired to stage a terrorist attack on a planned white supremacist rally with the intent of inflicting mass casualties in the Los Angeles area, according to federal prosecutors.

Mark Steven Domingo, 26, was arrested last Friday after he received what he believed was a live bomb that he intended to detonate at a Long Beach rally scheduled for Sunday. In fact, the supposed improvised explosive device was delivered to Domingo by an undercover law enforcement officer.

Domingo is charged with providing and attempting to provide material support to terrorists.

According to an affidavit, Domingo actively discussed with an FBI informant the possibility of attacking several possible sites, targeting Jews, police officers, churches and a National Guard armory before settling on the Long Beach rally.

In online posts, Domingo expressed his support for violent jihad. "America needs another vegas event ... something to kick off civil unrest," he wrote on March 3. That was an apparent reference to the Oct. 1, 2017, mass shooting in Las Vegas, in which the perpetrator killed 58 people before killing himself.

Domingo also expressed a desire to avenge the March 15 mass shootings at two mosques in Christchurch, New Zealand, in which 50 people were killed. "There must be retribution," he wrote, according to the affidavit.

Domingo had been deployed to Afghanistan between September 2012 and January 2013.

Domingo allegedly purchased 8 pounds of 3-inch nails for the planned IED because, he said, "they would be long enough to penetrate the human body and puncture internal organs," according to the affidavit.

At one stage of their plotting, according to the affidavit, the informant pressed Domingo for his attack plan, stressing that he didn't want to get caught.

"Your plan is just to go and get caught. That's your plan," the informant allegedly said.

Domingo allegedly replied, "Martyrdom, bro."

Domingo was taken into custody Friday night as he, the FBI informant and the undercover officer were conducting surveillance at the Long Beach park as part of their final preparations for the planned attack.

Copyright 2019 NPR. To see more, visit https://www.npr.org.