Story highlights

NEW: Spokesman: Kareem was in court last week, will have a detention hearing Tuesday

NEW: Official: He attended, cleaned carpets at Phoenix mosque Garland attackers went to

The two shooters were killed while attacking a controversial event in Garland, Texas

(CNN) —  

A federal grand jury has indicted an Arizona man for allegedly providing guns to, shooting with and talking through the plan to carry out last month’s attack outside a Prophet Mohammed cartoon contest, charging him on three counts and possibly opening the door for more arrests.

Only two men, Elton Simpson and Nadir Soofi, directly took part in the May 3 attack in the Dallas suburb of Garland, Texas. Neither of them made it into the city’s Curtis Culwell Center after being shot dead by an overmatched Garland police traffic officer who was part of the on-site security contingent. That officer, who was not identified for his own safety, was wounded but survived.

Until now, there has been no indication of any other person’s involvement nor any other known arrests.

A federal indictment filed last Wednesday and obtained Tuesday by CNN and other media outlets alleges Abdul Malik Abdul Kareem, also known as Decarus Thomas, played a significant role.

This includes allegedly giving firearms to Simpson and Soofi as far back as January 7, as well as traveling “to remote desert areas near Phoenix, Arizona, to practice shooting.” And in early May, the indictment claims that Kareem “did knowingly and intentionally transport firearms and ammunition” across state lines knowing that they may be used to commit murder in Texas.

After the attack, Kareem allegedly lied to the FBI on numerous fronts, including saying that Simpson and Soofi did not ask him to participate.

The court document suggests that Kareem is not the only person who, at least, knew about the planned attack.

Specifically, it states that he hosted Simpson, Soofi “and other persons known and unknown to the grand jury inside his home to discuss the Muhammad Art Exhibit and Contest and their plan to travel from Phoenix, Arizona, to Garland, Texas, to conduct an attack.”

Authorities haven’t identified who those people were or whether they, too, will face charges in the case.

Cleaned carpet at same mosque as 2 gunmen

While it’s not clear how long Kareem has been in custody, he had first court appearance late last week, said Cosme Lopez with the U.S. Attorney’s Office in Arizona’s capital.

He was detained in Phoenix on Tuesday, ahead of a planned detention hearing at 4 p.m. (7 p.m. ET), according to Lopez.

That city is home to the Islamic Community Center of Phoenix, which Simpson and Soofi attended for a time – a fact that led to a raucous but nonviolent rally and counter-protest late last month. The event’s organizer, Jon Ritzheimer, made no bones about his contempt for Islam and timed it to take place as Friday evening prayers took place inside the center.

Kareem went to the same mosque for a few years, its president,Usama Shami, told CNN. He “wasn’t somebody you would see regularly,” though he did clean carpets at the center.

“I never had any conversations with him outside of cleaning the carpet,” Shami said.

ISIS had claimed responsibility for attack

Whether Kareem, Simpson and Soofi got to know each other and like-minded people through the mosque is one big question. Another is whether they and others belonged to any organization outside of the Islamic Community Center, including a terrorist group that has attacked Americans and U.S. interests in the past.

What we know about Elton Simpson and Nadir Soofi

One such name that comes to mind is ISIS.

The Islamist extremist group began taking over large swaths of Iraq and Syria in early 2014, ruthlessly imposing its will – with widespread killings, rapes and enslaving of innocents – on those who don’t submit. Such tactics have drawn the ire of the U.S. government, which has taken a leading role in supplying Iraqi forces and conducting a military air campaign against ISIS targets.

In fact, ISIS applauded and said it was behind the Garland, Texas, bloodshed. But it didn’t offer proof, leaving U.S. officials with the view the group was attempting to be “opportunistic” by making a claim that allows it to say that it has attacked on American soil.

That said, it should be noted ISIS members aren’t the only who might have taken offense to the May event in Garland.

The Quran, Islam’s holy book, does not explicitly bar portrayals of Mohammed. But the religion has long discouraged any such images to avoid temptation toward idol worship, with many Muslims’ thus finding such depictions extremely offensive.

Most express these views peacefully. But there are exceptions, such as the January attack on the Paris office of Charlie Hebdo – a satirical magazine that drew derision for its publication of cartoons featuring Mohammed.

Notably, authorities found an ISIS flag in the hideaway of one of the Paris gunmen. Yet another group, al Qaeda in the Arabian Peninsula, claimed that it engineered the attack over years of planning.

The Charlie Hebdo carnage, in which 12 people were killed, sparked an outcry worldwide. Some people saw the attack as evidence of the depravity of radical Islamists and, in its aftermath, felt compelled to champion free speech even more. And it led to events like the one last month in Garland, which conservative Iowa Republican Rep. Steve King called “a robust demonstration of freedom of speech (that) we have to do.”

CNN’s Deanna Hackney and Sara Butler contributed to this report.