A Plano teen suspected of plotting an ISIS-inspired mass shooting at Frisco's Stonebriar Centre mall may not have entirely ruled out an attack on his high school.

Less than two weeks ago, Matin Azizi-Yarand was taking photos of fellow students at Plano West Senior High School and sending them to his supposed partner in crime.

Matin Azizi-Yarand is being held at the Collin County Detention Center. (Collin County Jail)

"Sitting ducks" is what the 17-year-old called them, according to documents obtained Thursday.

Authorities say they recorded a series of messages over five months about the teen's plans to commit a violent attack with others. Those "others" turned out to be two FBI confidential sources and one FBI undercover employee.

Azizi-Yarand "made clear that his attack would be on behalf of ISIS," according to affidavits related to the teen's arrest this week.

Most of the teen's messages revolved around a mass shooting at Stonebriar Centre, documents state. The teen had become familiar with the mall's layout. He scouted out security and police on patrol there. He even visited the crowded mall with one of the confidential sources.

"I'm not getting martyd [sic] without you," Azizi-Yarand told the source at one point, according to affidavits.

Authorities started tracking the teen's messages in various mobile applications in December. He told the source in a message on Dec. 19: "School is a perfect place for an attack. Crowded and close quarters. Lol. Even a blind man could take 10 easily. Just fire where u hear screams."

Azizi-Yarand was still discussing a possible school shooting as recently as April 20, one document states. The teen was exchanging messages with the FBI undercover employee that day. He sent along photos of various students, "describing them as 'sitting ducks' when discussing the possibility of an attack at the school," a search warrant affidavit states.

Plano ISD did not respond to a request for comment. An email to parents from the district's security director Wednesday said authorities confirmed that "the offense for which the student was arrested was unrelated to Plano West, Plano ISD or any fellow students."

Azizi-Yarand is being held at the Collin County Detention Center in lieu of $3 million bail. He faces charges of making a terroristic threat and criminal solicitation of capital murder of a Texas peace officer. If convicted, he faces up to life in prison.

He declined an interview request Thursday. The teen's father, reached by phone, also declined to comment. He said the family was in the process of hiring an attorney to represent his son.

The case is being investigated by the FBI along with Frisco and Plano police. The Collin County district attorney's office will prosecute the case in state court with assistance from the U.S. attorney's office for the Eastern District of Texas.

Authorities executed a search warrant at the teen's Plano home on Tuesday. They were looking for electronic devices. They seized a computer, a thumb drive, two cellphones, an Xbox 360, an Xbox One, a Nintendo Wii and a laptop computer, according to a property receipt.

Stonebriar Centre in Frisco was targeted by Matin Azizi-Yarand of Plano, who authorities say was plotting a mass shooting during the observance of Ramadan. (Louis DeLuca / Staff Photographer)

A separate search warrant allowed authorities to seize an iPhone 7 the teen had with him at school when he was arrested shortly before noon Tuesday. Documents state the teen used at least three separate mobile messaging applications to discuss his plans.

His smartphone had been banned from one of the apps, one affidavit stated. So the teen got another phone so he could communicate on that app "to find like-minded brothers to assist with the attack," the affidavits state.

Possible legal angles

No firearms were found at the teen's house, according to receipts attached to the search warrants.

That could become key in his defense. Much of the evidence rests on the teen's messages about what he planned to do. He also sent photos and documents to the FBI sources. But he never carried out an attack.

"You're essentially punishing or criminalizing speech," said defense attorney Mitch Nolte, who is not connected to the case. "Yes, you've got a right to free speech. But every right does have restrictions."

Matin Azizi-Yarand, 17, of Plano was arrested Tuesday at Plano West Senior High School.

The criminal case will likely revolve around not only whether the teen made the threats but also whether he had the means to carry them out, Nolte said.

"I understand that they err on the side of caution in charging these kids or adults," he said. "That's very understandable these days. But a lot of times the evidence is not sufficient. ... You've got to prove that they had the intent to threaten, to terrorize, to harass, to scare or whatever."

The messages Azizi-Yarand sent to the undercover employee "consistently pointed to committing a violent attack in the United States," the affidavits state. The messages also discussed "the supplies they would need to carry out the attack," the affidavits state.

The teen mailed a prepaid card for $500 to a post office box supplied by the undercover employee, affidavits state. He also mailed two separate envelopes of cash totaling $990, according to the documents. The money was supposed to be used to buy weapons and tactical gear, according to the affidavits.

The employee asked why the teen didn't buy the items himself. "Matin stated that his mother would be able to track his finances and see what he had purchased," according to one affidavit.

Authorities who searched the teen's Plano home seized several electronic devices. No firearms were found at the home. (Louis DeLuca / Staff Photographer)

By late March, the teen said in messages that he had selected Stonebriar as his target for a mass attack during Ramadan to limit the number of Muslim casualties, according to affidavits. Ramadan is Islam's holiest month. This year's observance begins May 15.

Messages talked of using automatic rifles and having plenty of ammunition. In an April 18 message, the teen allegedly stated: "My rifle needs to be pretty and cool looking // put an I love America sticky on the side."

Police allegedly targeted

The teen also allegedly plotted to kill police. According to the affidavit, the teen sent a series of messages while checking out the mall one day. "Counted 3 security // 1 cop upstairs with an actual gun // In movie theatre area // Yes yes real cop real gun // Notpretend cops // He's not gonna super hero and dome [sic] us all // if you'd want we could take him out first // Shouldn't be a problem."

Another message discussed the mall's movie theaters. According to the affidavit, the teen stated: "I'd probably take them [movie viewers] out into the light // And line them up for execution // Unless they're a kid // Or old."