CHICAGO (AP) — It had the trappings of an actual extremist website: Photos of gun-toting fighters and a flowery exhortation to, "Come and join your lion brothers ... fighting under the true banner of Islam."

Except, it wasn't what it seemed.

It was a sham site constructed and controlled by the FBI with the aim of snaring terrorist wannabes in the virtual world before they could carry out real-world harm.

Abdella Ahmad Tounisi, 18, was arrested last week on a terrorism charge stemming from the sting operation. He made a brief court appearance Tuesday in federal court in Chicago.

The American-born man from Aurora is accused of seeking to join al-Qaida-affiliated Jabhat al-Nusrah, which is fighting the Syrian Bashar Assad regime in a bloody civil war.

Critics say the use of such sites raises questions about whether authorities are overreaching, wooing impressionable youth to contemplate crimes that otherwise wouldn't cross their minds.

"These sites can end up creating crimes," said Phil Turner, a former federal prosecutor-turned-defense attorney in Chicago. "Real terrorists don't need to go to a website for contacts. They have real contacts."

Federal investigators, he added, sometimes favor Internet stings because they are less costly and less labor intensive than traditional stakeouts.

"From your office computer, you can get millions of cases like this — sucking people in," he said. "But it diverts our attention from the real terrorists."

Others disagree.

Mike Fagel, a Chicago-based security consultant, asks who, if given the chance, wouldn't have wanted to catch the Boston Marathon bombing suspects plotting online before they carried out their attack.

"These are valid tools," Fagel said about the sites. "As an emergency planner guy, if I can prevent something from happening, I don't have to worry about response and recover."

And given how terrorism is evolving, the Internet is a logical place to hunt for potential attackers, he added.

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"We are seeing younger and younger assailants," he said. "And they operate on the Internet."

Authorities have also noted that it's not visiting such sites or fantasizing about acts of terrorism that's the crime. The crime is acting on those fantasies and taking specific steps to make it happen.

Tounisi's steps, authorities say, included trying to board a plane in Chicago.

He was arrested at O'Hare International Airport Friday as he prepared to start the first leg of a trip that he allegedly hoped would eventually hook him up with the al-Qaida-affiliated group in Syria.

Tounisi is charged with one count of attempting to provide material support to foreign terrorists. If convicted, he faces a maximum 15-year prison term. His attorney, Molly Armour, declined comment on Tuesday.

Despite his orange jail garb and shackled ankles, Tounisi looked younger than his 18 years at his court appearance, during which a judge delayed a decision on bond. Later, he cast a worried look at his parents sitting nearby on a spectators' bench.

It was only weeks ago that he allegedly came across the site.

What he saw written across the home page allegedly signaled to Tounisi that he had found what he'd been looking for. "A Call for Jihad in Syria," it said in both English and Arabic.

The site not only offered to hook up would-be fighters with terrorists, it offered advice on how users could cover their Internet tracks from law enforcement, the detailed federal complaint explained.

"We are aware of (non-Muslims') tricks and the behavior of their unjust governments," the site said.

As some point, Tounisi allegedly took the bait.

In an April 1, 2013, email to an FBI agent posing as a terrorist recruiter, Tounisi comes across as earnest and frank, including about how some might see his youth and 5-foot-6 stature as an impediment.

"Concerning my fighting skills, to be honest, I do not have any," he allegedly wrote. "I'm very small ... physically but I pray to Allah that he makes me successful."

Not to worry, the FBI responds encouragingly in an email back to Tounisi.

"We have trust in Allah that you will fight and do your Jihad as a true (believer)," it said.

While he is accused of taking steps to further his desire to fight in Syria, his online searches also seem to convey concern about the legal implications. According to the complaint, for instance, he searched the phrases "providing material support what does it mean" and "Terrorism Act 2000."

Joan Hyde, a spokesman for the FBI in Chicago, declined comment Tuesday, saying the agency doesn't comment on ongoing cases.

The federal complaint suggests, however, that federal authorities don't want to hang their whole case on allegations Tounisi acted on what he viewed on the site.

It also alleges he was a close friend of Adel Daoud, a Chicago-area teen arrested last year on charges he tried to detonate a device he thought was a bomb outside a downtown bar. The complaint contends the two friends even discussed potential targets Daoud could hit.

Federal authorities don't accuse Tounisi of participating in the alleged attack planned by Daoud. But broaching his relationship in such detail may help prosecutors counter any future claim Tounisi stumbled onto the site and into the alleged crime by sheer naiveté.

Ironically, Tounisi allegedly opted out of Daoud's plot because he sensed — in that instance, one year before his own arrest — that something didn't feel right: He had concluded, according to the complaint, that Daoud's key contact may have been working for law enforcement.

In filings after Daoud's arrest, prosecutors acknowledged that the contact was, in fact, an FBI informant.

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Follow Michael Tarm at www.twitter.com/mtarm