(CNN) Harlem Suarez grabbed a jalapeno pepper from his plate and took a big bite. The heavily tattooed Cuban-American crepe-maker was eating dinner with two new friends, Shariff and Mohammed, at a Denny's in Key West on a warm June night. Suarez wanted to impress them but they laughed instead, joking in Arabic that he seemed suicidal.

"You've got nothing to prove, man," said Mohammed, as Suarez's eyes welled up with tears from the heat of the pepper.

Suarez did have something to prove. He wanted to convince Mohammed and Shariff that he was a devout jihadist with a grand plan to rain hell on Key West.

Never mind that Suarez had tried and failed repeatedly to make contact with ISIS recruiters abroad, according to court documents. He spent most of his downtime lifting weights at the gym and partying at kitschy bars on Duval Street.

Before long he'd be one of only two Americans sentenced to life in prison by the US government for plotting terror attacks on behalf of ISIS.

The 23-year-old high school dropout had cultivated various outlaw personas in the past, trying to make himself look like a gangster or a drug lord, according to interviews with his parents and friends in the Miami Herald. He legally owned three guns: two Glock semiautomatic pistols and an AR-15 rifle. His rap sheet was a lengthy but underwhelming array of traffic infractions and parking violations.

In 2015, Suarez's online persona took a dark turn. He created a Facebook profile under the name Almlak Benitez and uploaded violent jihadist propaganda. His account was suspended at least four times because of graphic content, Suarez boasted, but he found ways to restore the page. Suarez had searched Google for ISIS T-shirts, flags and other merchandise. He sent about 200 Facebook friend requests seeking out "brothers" sympathetic to the cause. His nickname was Black Angel of Death.

"stad up with us my brother stand up with the black flag an The ak with 10 mag fight with us be a gangster with us kill our enemies and convert to Islam now in usa," he wrote on Facebook.

One Facebook user accepted Suarez's friend request because he saw they had a mutual friend. He was alarmed by the images and rhetoric on Suarez's page, so he notified the Palm Beach County Sheriff's Office and gave screen grabs to the FBI. Within weeks of the initial tip from the Facebook friend, the FBI had a surveillance team following Suarez around the clock. At least 20 agents surveilled Suarez each day and sometimes 10 to 20 extra FBI employees were brought in to help keep tabs on him, according to court testimony. Mohammed, one of Suarez's dining companions at Denny's, was a paid FBI informant who specialized in terror cases. Shariff was an undercover agent posing as an ISIS supporter who knew a bomb-maker. They were both wired for sound and video as they joked about spicy peppers at the chain restaurant that calls itself "America's diner," famed for its big breakfasts and epic menu.

Mohammed said, "Eating those jalapenos is a struggle, it's a jihad."

As the three laughed, Shariff praised Suarez, "He said he didn't know any Arabic (but) he knows 'jihad.' "

Suarez didn't know Arabic. Nor did he recognize the name of ISIS' leader, Abu Bakr al-Baghdadi. Mohammed taught him about al-Baghdadi and introduced him to the terror group's handbook, "How to Survive in the West." Mohammed told Suarez he had camera gear and said they should make a recruiting video. The two wrote the script at Burger King and filmed it in a roach-laden room at a Knights Inn in Florida City.

Mohammed alerted Suarez that ISIS had called on its followers to conduct attacks on July Fourth events, according to court testimony from the informant. That's when Suarez started talking about blowing up police cars on the holiday.

"If we can learn how to work it out, we can in one night, we can hit more than 10 targets," Suarez said at Denny's. "Another month, we can hit like another 10 in another city. Now if we have more of our brother helping us, they don't have to be that close. ... In the future, we can have everyone together for the fight."

Over the course of dinner and late into the night, the informant and the undercover agent tried to get details about Suarez's plan.

Harlem Suarez, in a Facebook selfie

"Brother, you have some great ideas," said Shariff. "But you gotta have that focus and I'm wondering what specific target."

"Cops," said Suarez. "I will go for cops."

Suarez told Mohammed and Shariff that he was interested in conducting a domestic attack because traveling overseas was too costly.

"What city were you trying to go to?" asked Shariff.

"Iraq," Suarez replied.

"I'm saying...no, what city were you going to fly into?" Shariff asked.

"What do you mean?" Suarez replied.

"Just you're gonna fly directly to Iraq," Shariff said.

"But ... the ticket's like five thousand dollars," said Suarez.

"Jeez, where'd you look at? At what site?" asked Shariff.

"Internet," Suarez responded.

The meeting concluded with Shariff agreeing to talk to his associates about the purchase price for a grenade and a bomb.

But Suarez didn't try to blow up police cars on July Fourth. He went out drinking with his friends instead (trailed by the FBI's surveillance team).

Later in July, an undercover agent posing as a bomb-maker named Omar met Suarez in the parking lot of an Italian restaurant in Key West and gave him an inert explosive device custom-built in an FBI lab. Suarez idly fiddled with the fake bomb in Omar's car.

"Don't (expletive) throw it around," said Omar. "Don't use it as a (expletive) football or anything."

"We need young warriors like you," Omar said, just before Suarez exited the car and was arrested by the takedown team. Suarez was charged with attempted use of a weapon of mass destruction and material support of ISIS.

At least 60 FBI employees participated in the sting, including a 10-member evidence response team, a computer analysis response team, technicians from the agency's Hazardous Devices School in Huntsville, Alabama, and chemists at FBI headquarters in Quantico, Virginia. Suarez was convicted after an eight-day trial and sentenced to life in prison with no possibility of parole. Before the trial, he turned down a plea deal that would have capped his sentence at 20 years.

Suarez's trial attorney, Richard Della Fera, said it was a waste of taxpayer money to conduct such an elaborate investigation into an individual who had no proven ties to ISIS.

"All of these resources, ladies and gentlemen, just to reel in this little fish," Della Fera said during his closing argument. "Now, they'll say we had to take this seriously because of the things that he was saying on Facebook and we didn't know who we were dealing with. So far so good. But as the government got further and further and further into this investigation, didn't they have to know that what they were dealing with was a somewhat slow, somewhat naive kid?"

A photo of Harlem Suarez included in court documents

Assistant US Attorney Marc Anton said the fact that Suarez ultimately took possession of the (fake) bomb justified the FBI's efforts.

"The FBI did exactly what the FBI is trained to do," Anton said in response to the defense's closing argument. "They continue to investigate to determine exactly what type of threat Harlem Suarez was. And what did they find? He was exactly the type of threat that they were worried about. And he continued to re-engage and he continued to show up and he took possession of a bomb."

The FBI's counterterrorism/counterintelligence unit has a workforce of more than 25,000 employees on its payroll, according to the Justice Department.

It's a sprawling, sophisticated law enforcement division tasked with stopping terrorists before they act. That often entails going undercover to test suspects, giving them the opportunity to participate in a plot and seeing how far they'll go. About two-thirds of ISIS cases have involved sting operations with undercover agents and/or paid informants, according to a CNN review of arrests since 2014. Five out of 119 ISIS arrestees were busted with fake bombs furnished by the FBI.

Civil liberties advocates have criticized the FBI for targeting vulnerable people susceptible to manipulation because of mental illness or intellectual disabilities. They say that individuals who lack the resources or faculties to carry out devastating attacks on their own are getting caught up in labyrinthine government fictions. According to a Human Rights Watch study of 27 post-9/11 terror investigations, at least eight defendants showed signs that they were struggling with serious psychological issues or intellectual impairment.

The counterargument is that terror recruiters look for people with those very traits. Violent jihadists need not be master tacticians or Merlins with improvised explosives to pose a public safety threat, according to Ali Soufan, a former FBI agent and author of "The Black Banners: The Inside Story of 9/11 and the War Against al Qaeda."

"Many terrorists are literally idiots," Soufan wrote in a Wall Street Journal book review of "The Terror Factory," by Trevor Aaronson. "But that doesn't mean that they aren't dangerous, and if al Qaeda gets their hands on them, they will utilize them."

On December 11, ISIS adherent Akayed Ullah detonated a malfunctioning pipe bomb at the Port Authority in New York. The former taxi driver used Velcro and zip ties to holster the device, which was packed with nails and screws. It did not explode but smoldered instead, burning Ullah and filling the corridor with smoke. Five people suffered minor injuries.

Ullah joins the ranks of other hapless yet malevolent post-9/11 attackers, a group that includes the Christmas Day underwear bomber, shoe bomber Richard Reid and wannabe dirty bomber Jose Padilla. Ullah is the second person who's attempted to blow up Times Square over the past decade. The first was Faisal Shahzad, an al Qaeda supporter who tried to ignite a car bomb on Broadway in 2010. He set his vehicle on fire instead and his plot was foiled by street vendors who reported smoke to police.

Soufan wrote that undercover operations are a necessity to root out and stop people like Reid and Ullah long before they get the chance to enter crowded, confined spaces with makeshift explosives. Ullah was indicted on six charges including providing material support to ISIS, using a weapon of mass destruction and conducting a terrorist attack against a mass transportation system. He has pleaded not guilty on all counts.

"As you can't prosecute someone just for professing a desire to kill Americans, and you can't read minds to determine if they really intend to carry out their threats, either you wait to see if the real al Qaeda gets in contact, and hope you can track them, or you intercede," wrote Soufan.

Notable post-9/11 domestic terror stings include a plot to attack the Fort Dix Army Base in New Jersey, an attempt to bomb a Christmas tree lighting ceremony in Oregon and a conspiracy to blow up Jewish centers in the Bronx. Each of these cases led to convictions, along with controversy. Advocacy groups including the American Civil Liberties Union and the Center for Constitutional Rights have filed legal challenges claiming that the FBI largely constructed the plots via undercover operatives and entrapped the suspects. Thus far, none of the convictions have been overturned.

Suarez's public defenders filed a brief in October with the 11th US Circuit Court of Appeals, arguing that a life sentence is cruel and unusual punishment for a young, gullible, first-time offender with no history of violence. They argued that Suarez has a low average IQ and cognitive deficiencies, according to a clinical assessment by a neuropsychologist. The brief refers to the ban on life sentences for juvenile defendants. In a December 8 filing, the government responded that Suarez had been deemed competent to stand trial and he is not a juvenile. Oral argument in the case is set for April 25 at the federal courthouse in Atlanta.

The trial judge described Suarez as "inept." He pointed out, however, that criminal intent was present, regardless of Suarez's capabilities, or lack thereof.

"How does his ineptness balance in here?" said Judge Jose E. Martinez, during Suarez's sentencing hearing. "How does his apparent inability to do what he was planning on doing affect this? I don't know that he was unable to do it. I think it would have been difficult for him because I don't think he's a particularly skilled bomber. But I think that he could have done this and he could have caused a tremendous amount of problems. And his communications are encouraging other people. He does have a lack of communication skills. That doesn't change the fact that he was really trying to do it and that he was really opening himself up to exactly what happened to him, which is that he got busted."

Della Fera said the FBI should have intervened after his client and Mohammed made the recruitment video. Prosecutors argued that they needed to see whether Suarez was just making empty threats or if he would engage in violence given the opportunity.

"This individual had an AR-15, two Glocks, bulletproof vest, was ordering another gun and was talking about committing attacks for ISIS," said assistant US Attorney Karen Gilbert. "If we're there, we can control the scenario like the bomb. But if he had decided one day to just go use his guns, we may not have been able to stop them. Thank goodness he didn't. Timing helps us sometimes. We just get lucky sometimes."

It wasn't just luck. At various points throughout the three-month investigation, Suarez bailed on Mohammed and Shariff. For weeks-long stretches, he wouldn't answer the phone or respond to increasingly desperate texts, according to trial transcripts and other court documents.

Della Fera said Suarez wanted to distance himself from Mohammed and Shariff without cutting them off completely, fearing for his family's safety. Trying to get away from ISIS is like trying to get away from the Mafia, Della Fera said.

"You don't walk away from ISIS without them coming back for some kind of retribution," Della Fera said during his closing argument. "You don't walk away from these people, because what do they think? What does (Suarez) think they think? 'Hey, why is this guy not calling me? Hey, we met with this guy. He's seen our faces. What if he goes and snitches on us? Maybe we need to take care of a guy who could possibly snitch us out, because now he's dodging us.' "

On July 6, three weeks before Suarez's arrest, Mohammed reconnected with Suarez and said Shariff's friend could make a nail bomb in a backpack for him for $200. The price would be slashed to $100 if Suarez supplied the nails, a cellphone as a detonator and a backpack.

"OK but wait, I don't like, I don't get it," said Suarez. "Why it need to go inside a backpack?"

"It has to look innocent, you know what I'm saying," Mohammed said. "Someone leaves the backpack."

Suarez eventually settled on a plan to bomb a nearby beach.

"I just call and the thing is gonna make ... a real hard noise from nowhere and like people are gonna be like what, where this (expletive) came from," said Suarez.

Just before sentencing Suarez to life in prison, Judge Martinez told Della Fera it was a tough call because the defendant's shortcomings were apparent throughout the trial. The judge ultimately determined, however, that the maximum penalty was fitting as a deterrent.

"There are a lot of, I don't know what the right word is, people (who) don't think the same way as other people think -- let me put it that way -- running around loose," Martinez said. "If they start plotting in their own minds that they're going to assemble a weapon of mass destruction and set it off at Smathers Beach or set it off on Stock Island or set it off wherever it is that he finally decided that he was going to set it off, and actually go to a meeting and take it and listen to the instructions, albeit not very well, but listen to the instructions on how to assemble it and how to blow it up, thinking that he has a bomb and that he's going to put nails and whatever it was, ball bearings, I know that various things were mentioned at various times, that's just nutty. I mean, it is dangerous. It's off the wall, Mr. Della Fera. It's too much."