Halfway through 2014, three Arizona men were falling under the sway of the Islamic State group, authorities say.

The trio watched videos depicting violence by jihadists, tried to get pipe bombs, planned an attack at a Prophet Muhammad cartoon contest in Texas last year and researched travel to the Middle East so they could join Islamic State fighters, investigators say.

Two of the men brought semiautomatic rifles and an Islamic State flag to the May 3 contest featuring cartoons deemed offensive to Muslims and died in a shootout with police before hurting anyone attending the event in suburban Dallas.

The third man goes on trial Tuesday in Phoenix in what is believed to be the first time the U.S. government has put a person on trial on terror charges related to the militant group.

Abdul Malik Abdul Kareem, a 44-year-old moving company owner, is accused of hosting the two gunmen at his home to discuss plans for the attack, going target shooting in the remote Arizona desert with the pair and providing the guns used at the contest.

Prosecutors say Kareem also encouraged Elton Simpson and Nadir Soofi to carry out violence in the United States in support of the Islamic State group and inquired about explosives to blow up a stadium in metro Phoenix during the 2015 Super Bowl.

Kareem denies the allegations.

It's unknown whether the thwarted Texas attack was inspired by the Islamic State or carried out in response to an order from the group.

Prosecutors paint a picture of three men being influenced by the group, which has amassed thousands of fighters around the globe and taken control of parts of Syria and Iraq while carrying out beheadings, mass shootings and other violence.

Six weeks before the cartoon contest, Simpson accessed an Islamic State list of residential addresses of U.S. military service members whom the group wanted attacked. Simpson and Soofi also drove to Yuma and elsewhere in Arizona near military installations after having discussed plans to attack a base.

FBI Director James Comey told lawmakers in December that one of the attackers exchanged more than 100 messages with an overseas terrorist in the days before the attack in Garland, Texas. Kareem's indictment says Simpson used social media to communicate with Islamic State extremists and other violent jihadists.

The U.S. Justice Department didn't respond to questions about the case.

"I believe the shooters were motivated by what they thought was the Islamic State, but I'm not sure they were directed by the Islamic State," said Scott Stewart, a vice president for the Texas-based global intelligence company Stratfor and a former U.S. State Department investigator who examined the 1993 World Trade Center bombing.

The U.S. government has charged 78 people with crimes related to the Islamic State group since March 2014, said Karen J. Greenberg, director of the Fordham Law School's Center on National Security, which tracks terrorism cases. While 24 people charged with crimes related to the radical group have pleaded guilty, no one has yet gone to trial on such charges.

Kareem and his lawyer, Daniel Maynard, declined requests for an interview. Maynard has previously said the case was trumped up and based largely on the work on an unreliable confidential informant.

Two days after the Texas attack, Kareem went to the FBI's office in Phoenix for an interview with investigators in which he denied any involvement. He was arrested five weeks later.

James Newman, Kareem's younger brother, told The Associated Press that his brother never expressed a radical political or religious view to him and is a victim of guilt by association with the two Muslims who carried out the attack. He vehemently rejects the government's portrayal of his brother as a supporter of terrorists.

Newman said Kareem was a Muslim throughout his adulthood, but his faith deepened over the last five years after he was jailed on a drunken driving conviction. He used his religion as a way to cope with his longtime struggle with alcohol. He abandoned his birth name of Decarus Lowell Thomas and legally became Abdul Malik Abdul Kareem in 2013.

"It probably wasn't the smartest decision to hang with these guys, but he was probably just building his faith," Newman said of Simpson and Soofi.

Kareem, sporting a shaggy salt-and-pepper beard and bound by handcuffs and a belly chain, has remained silent through his latest court hearings. Six deputy U.S. marshals stood watch in the courtroom during a late December hearing. He faces charges including conspiracy and conspiring to provide material support to a foreign terrorist organization.

Authorities say they first interviewed Kareem in a terrorism investigation in late 2011 and later searched his apartment when one of his roommates tried to get a fraudulent Arizona State University degree as part a plan for the roommate to gain admission into an Islamic university in Saudi Arabia.

During the apartment search, authorities say they found al-Qaida promotional materials on Kareem's laptop and an attached flash drive. Kareem has denied the flash drive was his. His lawyer unsuccessfully tried to bar prosecutors from using the promotional materials as evidence at trial.