The government has built a compelling case for guilt: Testimony has ranged from bombing survivors' dramatic accounts to fellow officers who found a rookie executed for his gun; from a frantic carjacking victim to a final showdown in a sleeping suburb that left a pressure cooker bomb embedded in a car door and sent bullets through the walls of a second-story bedroom.  Investigators have mined data from GPS devices and matched them to store receipts to track the purchases of the backpacks, BBs and 6-quart pressure cookers used to make two bombs detonated near the finish line of the Boston Marathon.  Prosecutors will likely rest their case against Dzhokhar Tsarnaev on Monday. And then Tsarnaev's lawyers will get their turn. Their presentation is expected to be brief; the defense admits he did it and doesn't dispute many of the facts, just how they are being spun.  This part of the story and who takes charge of the narrative could very well determine whether he spends the rest of his life in federal prison or is executed for his crimes. How did Tsarnaev come to be a bomber, and what role did his older brother, Tamerlan, play?  The story of Jahar Tsarnaev, as his friends knew him, is one of great expectations and crushing failure.  Jahar came to the United States from Russia when he was 8. He seemed to adapt to his new home more easily than other members of his family. He was popular and did well in high school. He was the captain of the wrestling team.  And then it all went off the rails. His parents divorced and headed back to Dagestan. He was adrift and flunking out of college.  Because of his poor academic performance, he lost his financial aid at the University of Massachusetts Dartmouth. He was still attending classes and living in his dorm room when he wrote a pitiful plea for reinstatement on January 24, 2013:  "This year I lost too many of my loved relatives. I was unable to cope with the stress and maintain schoolwork. My relatives live in Chechnya, Russia. A Republic that is occupied by Russian soldiers that falsely accuse and abduct innocent men under false pretenses and terrorist accusations.  "I am at a point where I can finally focus on my schoolwork. I wish to do well so one day I can help out those in need in my country, especially my family members."  Four days later, he texted a friend: "Come May I'm out." There would be no fifth semester of classes at UMass Dartmouth. His friend asked if he was finding a "wifey" and settling down. He responded that he's just trying to finish school.  "I mean there's 1 other option, bro  Only the most pious of Muslims get to Jannah. But there's a short cut, according to proponents of jihad: You can become a martyr.  "I got a plan," Tsarnaev texted.  "I'll tell you later about it."  Less than three months later, two bombs exploded near the finish line of the Boston Marathon, killing three people and injuring more than 250 others.  Was that Jahar's plan? If it was, what did he hope to achieve? Martyrdom? Paradise?  Prosecutors claim he was a self-radicalized jihadist who pored over militant writings, including an article, "How to Build a Bomb in the Kitchen of Your Mom."  It was found on his laptop and other devices, part of a full-edition download of Inspire magazine, a glossy English language propaganda tool put out by Al Qaeda of the Arabian Peninsula.  His laptop also held a downloaded copy of "Join the Caravan," a book written by Imam Abdullah Azzam, a founding member of al Qaeda who is considered the father of al Qaeda-style jihad.  From Inspire: "Can I make an effective bomb that causes damage to the enemy from ingredients available in any kitchen in the world? The answer is yes. But before how, we ask why? It is because Allah says ... every Muslim is required to defend his religion and his nation."  His audio collection included speeches and videos of al Qaeda propaganda master Anwar al-Awlaki, the U.S.-born Yemeni cleric who was known as the Osama bin Laden of the Internet until he died in a U.S. drone strike in 2011. Jahar's computer files contained a copy of al-Awlaki's "The Hereafter" and other, more militant writings.  Some of al-Awlaki's YouTube videos, found on the Tsarnaevs' computers and other devices, were set to nasheeds, the spiritual chants popular among young Muslims.  "Terrorism to go," an expert witness for the government called it. It's a trend in the social-media-savvy global jihad movement.  The movement embraces these primary concepts: Muslims are obligated to engage in jihad; killing nonbelievers is justified if Muslims are being persecuted; and all martyrs are rewarded with a special place in paradise.  With "terrorism to go," a recruit no longer needs to travel to a training camp, he now can find everything he needs to know "sitting on his computer in Mama's basement," said Matthew Levitt, who heads the Program on Counterterrorism and Intelligence at the Washington Institute for Near East Policy.  The trend towards self-taught radicalism reflects what Levitt calls "tectonic changes" in global jihad over the past decade. The biggest threat no longer comes from a spectacular 9/11-style attack by an organized al Qaeda cell. Attacks are now more likely to come from lone-wolf recruits. The attacks may be smaller, he said, but they will occur more frequently.  There's no world headquarters for global jihad, and no leader to speak of. It's more of an idea shared by a group of like-minded people, Levitt testified. The Internet and social media have made it possible for recruits to radicalize without ever meeting.  That was the appeal for the brothers Tsarnaev, who identified as Chechens, even through they were living in the United States and their parents were in the nearby Russian republic of Dagestan.  They might not be studious and pious, but they could still become good Muslims, Levitt said. They could still reach the highest level of paradise through the ultimate sacrifice: martyrdom.  The seed was planted more than a year before the bombings. Although it is not yet possible to know who started the discussion, or who downloaded the material first, it was all over both Jahar's and Tamerlan's devices.  Both felt deep disappointment at how their lives had turned out. And, according to Levitt, setbacks in life can leave a young person especially vulnerable to acting out on radical beliefs.  "Discrimination, getting dumped, an identity crisis" create the opening, Levitt said. "There's going to be some component of grievance, and some component of ideology, plus anger at things at home and internationally."  Jahar Tsarnaev wasn't known to be particularly religious or political in high school. He was more of a party guy. But his college years brought stress way beyond the usual growing pains.  The militant material started showing up on his computer, phone and iPod more than a year before the bombings. By the time he finished his freshman year, in 2012, his parents had left for Dagestan. He began to spend more time with Tamerlan, who had a wife and young child -- and full run of the Tsarnaev family's Cambridge apartment.  The defense acknowledges all of this, but points the finger at an influence more powerful than the Internet propagandists.  It was "one of those tough times of adolescence," defense attorney Judy Clarke told jurors. He became vulnerable to the influence of "someone he loved and respected very much: his older brother."  Tamerlan Tsarnaev, who was killed during the gunbattle with police in Watertown, may be absent from the defense table. But he's very much a part of this trial, even though prosecutors frequently object when the defense brings up his name.  Stephen Silva, Jahar's best friend since middle school, described Tamerlan's hold: Jahar looked up to his older brother, even if he acknowledged that others might find him harsh and rigid in his beliefs.  Silva never met Tamerlan and visited the family's Cambridge apartment just once. But Jahar warned him that his brother was "very strict, very opinionated" and would consider him an infidel because he wasn't Muslim.  "Did he tell you you don't want to meet his brother?" asked Miriam Conrad, another of Tsarnaev's attorneys.  "Yes he did," Silva responded.  Silva is no angel. He testified for the government under a plea deal he hopes will shave years off a sentence for gun and heroin-possession charges. Silva gave Jahar Tsarnaev the 9 mm Ruger the brothers used to shoot and kill MIT police officer Sean Collier. One of them -- Tamerlan's fingerprint was found on the weapon -- fired 56 shots at police during the showdown in Watertown.  Silva was shocked when he learned his friend had been involved in the marathon bombings. He never saw it coming. He said he told the FBI he believed Tamerlan was behind it.  Indeed, the defense made certain to point out every surveillance photo and record that shows Tamerlan Tsarnaev taking the lead. He walked ahead of his younger brother as they left the bombs near the marathon finish line. He was alone when he purchased two backpacks at a Target store the day before. The components used to make the bombs were found in his apartment, along with a target that had been "pretty shot up" with a BB gun, investigators testified.  Even before the defense starts its case, we've learned plenty about Jahar Tsarnaev. We've seen his texts and tweets, and how he surfed the Internet. We've seen his college transcript -- seven failing grades in four semesters. We've even seen the too-cute frogs and lily pads taped to his dorm room door.  Tamerlan is more of a cipher. He boxed and was a married father. Although he is portrayed as the more forceful, devout and radical of the brothers, we have heard nothing about any texts, emails or voicemail messages he might have exchanged with Jahar. We know only that they spoke briefly over their cell phones moments before and after the marathon bombs went off.  If the defense asserts that Tamerlan was the radicalizing force in Jahar's life, prosecutors maintain that Jahar was not who he seemed to be: that he led a double life as an amiable, slacker college student while immersing himself in literature promoting violence against "nonbelievers."  There's no way to know for certain whether he downloaded the militant material himself or loaded it from somebody else's hard drive. There's no way to be sure he even read it. But the footprints of what is said in these volumes written and spoken by radical clerics can later be found in his own writing.  Failure is at the heart of this case. The Tsarnaev family's American dream failed; Tamerlan's dream of boxing for the United States in the Olympics failed. And Jahar, the popular high school wrestler, was failing, too.  He expressed his political disillusionment in a text to a friend on November 6, 2012, one day before the presidential vote: "Elections are whatever. I want the lesser of two evils to win, which is Obama, but either way they're ... puppets of the system. Killing Muslims is the only promise they will fulfill."  His transcript over four semesters shows he quickly changed his plan to major in mechanical engineering after failing two chemistry classes and getting a D in calculus. But even after switching to a more relaxed liberal arts curriculum, he failed a math class and a critical writing course.  He raised his grade in the writing course to a B in the fall of 2012 but then failed three more courses -- Introduction to American Politics, Chemistry and General Psychology. He was retaking the politics and psych courses, as well as an ethics class at the time of the bombings.  During his testimony, Levitt drew parallels between the militant materials found on Tsarnaev's laptop and words he scrawled with a pencil on the blood-streaked sides of a boat where he sought shelter after the shootout in Watertown.  Levitt offered footnotes from the militant writings for key passages of what prosecutors have called Jahar's "boat manifesto," in which he asks God to make him a martyr like his brother:  "I do not mourn because his soul is very much alive. God has a plan for each person. Mine was to hide in this boat and shed some light on our actions. I ask Allah to make me a shaheed to allow me to return to him and be among all the righteous people in the highest levels of heaven."  Among the influences Levitt cited: Inspire magazine and "Join the Caravan," which promises paradise, 72 wives and other great rewards for martyrs and 70 members of their household.  "The audience is the American public," the expert said of Tsarnaev's writings. "This is an attempt to explain what has been done."  It would also indicate that the militant teachings of his jihad heroes weren't just in his computer.
A 19-year-old stoner who listened to Jay-Z, watched "The Walking Dead" and referred to himself as a "people person" came to embrace violent global jihad.