Prosecutors opened their case Wednesday against a man they portrayed as an Islamic State follower and the driving force behind a plot to attack an anti-Islam cartoon contest last year, calling him the leader of a team "set on mass murder."

Abdul Malik Abdul Kareem, a 44-year-old owner of a moving company, is believed to be the first person to stand trial in the U.S. on charges related to Islamic State.

He is charged with helping plan an attack last year at a Prophet Muhammad cartoon contest in Texas in which two associates were killed after they showed up at the event with semiautomatic rifles, bulletproof vests and an Islamic State flag.

Prosecutor Kristen Brook portrayed Kareem as being obsessed with Islamic State as it began a global terrorism menace last year, going so far as to indoctrinate a child in his neighborhood by showing him Internet videos of the group's militants burning a Jordanian pilot in a cage. She said he was instrumental in helping Elton Simpson and Nadir Soofi in their thwarted attack on the cartoon contest before the pair was killed by an officer.

"The defendant was the bankroller, trainer and motivator in the plot," she told the jury.

Kareem's lawyer rejected the government's characterization of him being the driver of the attack. Daniel Maynard said Kareem had no knowledge that Simpson and Soofi were going to Texas to carry out an attack.

"This is an overactive imagination for the government," he said.

The U.S. government began its case against Kareem by explaining to the jury the origins and methods of Islamic State and describing how he became an avid follower in early 2015.

Brook said Kareem, Simpson and Soofi watched terrorism videos, beheadings and Islamic State propaganda clips, and had a reverence for anything coming from Anwar al-Awlaki, the American-born cleric killed in a CIA drone strike in 2011 who remains an admired figure among radicals.

She said they originally wanted to acquire explosives to blow up the stadium hosting the 2015 Super Bowl and a nearby shopping center. When that plan failed to materialize, they allegedly set their sights on the cartoon contest in Garland, Texas.

Brook cited tweets by Simpson in which he posted a photo of al-Awlaki and said "when will they ever learn," after learning of more prizes available to people participating in the contest.

Kareem faces charges including conspiracy to support Islamic State. Brook said he knew Simpson and Soofi were followers of Islamic State but still helped them carry out the attack, including buying weapons and showing them how to shoot and clean the guns.

"The defendant was the third man on a team set on mass murder." she said. "Two were killed one remains."

The courtroom has become a new front against Islamic State as the government attempts to crack down on followers of the terrorist organization.

The U.S. government has charged 78 people with crimes related to Islamic State since March 2014, said Karen J. Greenberg, director of the Fordham Law School's Center on National Security, which tracks terrorism cases. A total of 24 people charged with crimes related to the radical group have pleaded guilty.

The first day of testimony in the Phoenix trial included a security guard and police officer describing the shootout in Garland last May.

Garland officer Gregory Stevens recalled seeing Simpson exit from their vehicle carrying a semiautomatic rifle, at which point he immediately drew his pistol and started shooting. Stevens said he fired off 14 rounds as he killed the two men, and remembers having a fear that Simpson was going to pull a pin from a grenade to inflict violence outside the event.

Bruce Joiner, a security guard who approached Simpson and Soofi moments before the attack, said Simpson had a smile on his face just before the shooting started. Joiner initially thought it was a prank but quickly concluded that wasn't the case.

"He had a smile on his face," said Joiner, who was shot in the leg during the attack. "It kind of caught me as one of those moments I remember."