At about 10:40 one morning last August, Mohammed Abul Barra rammed his ash-colored station wagon into a security gate outside the United Nations headquarters in the Nigerian capital, Abuja, knocking it off its hinges. Barra's 1996 Honda Accord then crashed through the main building's glass doors and slammed against the reception desk.On security tapes of the incident seen by Reuters, a guard peers into the car, evidently unaware that it is packed with explosives. The grainy footage shows a dozen or so people in the reception edge towards the vehicle. Over 10 seconds pass in confusion before one man seemingly realizes what is about to happen. He grabs the person next to him and darts towards the lift. But it's too late. Barra steadies himself, leans forward and the security screens blur into white fuzz.The FBI follows a forensic trailUS Federal Bureau of Investigation agents arrived in Abuja within days of last August's attack to help with forensic analysis of the bomb site. A report authored by those agents, Nigerian authorities and independent security teams, paints a portrait of a sophisticated operation.Barra was chosen because he was "low profile (and) well trained" and his attack was "well planned," says the confidential report, seen by Reuters. The car was packed with 125 kg (276 pounds) of manufactured explosives, including the plastic explosive pentaerythritol tetranitrate (PETN) and triacetone triperoxide (TATP) - both highly powerful and volatile, and more potent than easier-to-build fertilizer-based explosives.The explosives were used in a "shaped charge," which increases damage from a blast. Investigators believe the bomb probably consisted of both stolen factory-made explosives and home-made materials. "The only form of PETN that is commonly available is the core explosive in detonating cord," said Sidney Alford, a British explosives expert. "You can get detonating cord from the manufacturers, the army, or from blasting contractors in the demolition or quarrying industries."The failed 'underpants' bomber Faroup Abdulmutallan, a Nigerian accused of trying to blow up a Detroit-bound flight on Christmas Day 2009 in an al-Qaida-style attack, used TATP. Another would-be plane bomber, Richard Reid, had PETN in his shoe in his unsuccessful effort to blow up a flight between France and the United States in 2001.President Jonathan said Nigeria has evidence that Boko Haram members have held meetings in North Africa. Azazi, the national security adviser, said the advancement in Boko Haram's weaponry and tactics points to help and training from outside groups."We have evidence of meetings between Boko Haram leadership and outside groups," Azazi said, declining to give details. "We have evidence that some Boko Haram leaders are trained outside of Nigeria. Their methods, their bomb-making technologies - who taught them?"Boko Haram's militant beginningsNigeria, Africa's top oil producer, survived a brutal civil war in the late 1960s in which more than 1 million people died. Repeated rounds of violence since then, often between Muslims in the north and Christians in the south, have killed thousands more.The violent spasms are often fueled by politics, and so it is with Boko Haram.The group's official name is Jama'atu Ahlis Sunna Lidda'awati Wal-Jihad, meaning "People Committed to the Propagation of the Prophet's Teachings and Jihad." It earned its nickname from the teachings of its founder Mohammed Yusuf in the early 2000s, in the restive northeastern city of Maiduguri, the capital of Borno state.Yusuf argued that Western education, or "boko," had brought nothing but poverty and suffering to the region and was therefore forbidden, or "haram," in Islam. He began peacefully - mostly preaching - and quickly gained a following among disaffected young men in the northeast. But his anti-establishment rhetoric and hints that Boko Haram was building an arsenal of weapons also caught the attention of the authorities. In 2009, the police clamped down on sect members who were ignoring a law requiring motorcyclists to wear helmets. That sparked a furious backlash. Police stations and government offices in Borno were burned to the ground, and hundreds of criminals released in a prison break, as the violence spread across northern Nigeria.The government and army reacted with force; Yusuf was captured and shot dead in police custody. Five days of fighting left some 800 people dead.Boko Haram leaders still cite Yusuf's death as one of the main factors driving the insurgency. The group remains fiercely anti-government and anti-authority, and resentful of the decades of corrupt, poor governance that have impoverished its home region."You would never have believed the Boko Haram phenomenon came from these beginnings," said Shettima Dikwa, a doctor at the University of Maiduguri. Dikwa is one of a number of professionals in the city frustrated at the way Nigeria's government and military have allowed the insurgency to escalate. Like others, he says local politicians sponsored armed thugs to help disrupt the 2007 election and then abandoned them, creating a fertile recruitment field. The governor of Borno state has denied these allegations.Boko Haram's attacks have intensified since President Jonathan took power last April, in the country's cleanest election since the end of military rule in 1999. Jonathan pledged to fight graft and attract investment. But he is a Christian southerner, and in the eyes of many Muslim northerners it was a northerner's turn to rule.Striving for global jihadThat backdrop doesn't explain how the group went from drive-by shootings and crude petrol bombs to shaping explosives for suicide missions against the United Nations.A video posted on YouTube on January 11 suggests the group's leadership would like to be seen as part of a global jihad. Abubakar Shekau, who has run the group since Yusuf was killed, appears in the 15-minute tape wearing a camouflage bullet-proof jacket, sitting in front of two Kalashnikov rifles. His beard, headscarf and hand gestures recall the style of video pronouncements made by the late al-Qaida leader Osama bin Laden. But Shekau's message hits local notes."The reason why I am giving this broadcast is the recent comments of Goodluck Jonathan about us and that of the leader of the Christians and other statements by others, describing us as a cancer to Nigeria. We are neither a cancer nor a disease. If people don't know us, God knows us," Shekau says. He then goes on to cite common complaints about Nigerian politics. Most of the public evidence about what Boko Haram wants and how it operates comes from its avowed spokesman, Abu Qaqa, a mysterious figure who often pops up after an attack to claim responsibility and explain the motives.Speaking by phone to a handful of reporters in Maiduguri in November, Abu Qaqa spoke of the links between al Qaeda and Boko Haram. "We are together with al-Qaida," he said. "They are promoting the cause of Islam, just as we are doing. Therefore they help us in our struggle and we help them, too."But Qaqa offered no concrete details of those ties; the rest of the conversation focused on local issues. He said the group isn't affiliated with Nigerian political parties and described the sect's anger at the governor of Borno state. In claiming the recent Kano attacks, which killed at least 186 people, he cited the killing and arbitrary arrest and detention of Boko Haram members.Global or local?Nigerian and Western security experts believe a small, increasingly ambitious and sophisticated group of extremists controls the very top of the group. A handful of those members have received training outside Nigeria, including from AQIM.Nigeria-based security sources who track Boko Haram told Reuters that members of the group have been going to training camps with brigades of Algerian AQIM for the past six years. Small units of five or six members train at a time; no more than a few dozen have been trained in total, the sources said.The foreign minister of neighboring Niger told Reuters last week that members of Boko Haram received explosives training at AQIM camps in the Sahel region, which runs along the southern edge of the Sahara desert. The UN Security Council said this month that it had been told that Boko Haram members had received training in AQIM camps in Mali.Experts say the group has become a convenient cover for opportunists. Criminals, political thugs and gangs hide beneath the umbrella of Boko Haram, making it hard to judge its size and scope.Most of its foot-soldiers are disillusioned young men who have only loose ties to religious ideology, and are easily drawn in because there are little or no opportunities elsewhere. Jonathan has begun to acknowledge this, telling Reuters last week that the government would "revitalize" northern agriculture to provide jobs for youths who might otherwise be "recruited" by Boko Haram.Aisha Alkali, a human rights campaigner in Maiduguri, says young men in northern Nigeria feel forced to adopt violence to defend themselves. "If you push people to the wall, if you leave them with nothing and take everything, where will they go?" asks Alkali, shrouded in a traditional black abaya and burka with only her eyes and impeccably manicured hands showing. "You make people something they were not."The government cracks downSoldiers patrol the streets of Maiduguri in large numbers these days. By day, they hunch in roadside bunkers; at night, they regularly fight with Boko Haram units. Bomb blasts and gunshots punctuate the dark.Amnesty International says the joint military task force (JTF) in the city has been behind dozens of unlawful killings there, further stirring the unrest. A report by the human rights watchdog says houses have been raided and burned by the JTF.One of the JTF commanders in Maiduguri told Reuters there had been "excesses," but said mostly the military were doing a good job under difficult conditions. Yirami Bwala, a 42-year-old shop owner, lost his 18-year-old son Markus in a Boko Haram bomb attack in Maiduguri in January. "Most Boko Haram members are just a bunch of illiterates who have been misled about their religion and what tolerance is all about," he said a day after the attack. "The military only make things worse by robbing people and attacking innocent, peaceful people."More than a quarter of Nigeria's 2012 budget has been allocated to security spending. But with the number of attacks up - at least 250 people have been killed in the first three weeks of 2012 alone, according to Human Rights Watch - criticism of the way Jonathan has handled the violence is growing.Searching for a faceless enemyPresident Jonathan told Reuters that Boko Haram militants have infiltrated the military, police and his own government. He sacked the chief of police and his six deputies last week, after the key suspect in the Christmas Day bombings escaped less than 24 hours after being arrested, in what Nigerian security sources said were "unusual and suspicious" circumstances.The leader of the nation of 160 million people has also said that tackling Boko Haram could be worse than Nigeria's civil war, if only because the enemy is faceless and unknown. Some analysts believe Boko Haram may be targeting Christians to trigger a religious conflict.Nigeria has been here before. In 2009 it ended a militant insurgency in the southeastern Niger Delta by offering an amnesty. The government hints that a new broad political settlement may be on the cards. But dealing with a splintered and secretive group like Boko Haram will be difficult.Olusegun Obasanjo, a former president and a southern Christian, visited the family of Boko Haram founder Yusuf last September for peace talks. Days later, gunmen killed Yusuf's brother-in-law. Boko Haram denied involvement in the killing. But someone wanted the dialogue to end.The suicide strike left 25 people dead and the UN headquarters in tatters. It also drew global attention to Boko Haram, the militant group from northern Nigeria which has claimed responsibility for the attack and a string of bombings since then that has killed hundreds. As the bombings have grown in frequency in recent months, the Nigerian government and Western security officials have begun to grapple with the exact nature of the threat. Is Boko Haram just the latest in a long list of violent spasms in Nigeria, or is it the next battalion of global jihadists, capable of thrusting Africa's most populous nation into civil war?The answer to that is not simple. There is evidence - some of it detailed in this story for the first time - that elements of Boko Haram have received training from foreign militant groups, including North Africa-based al-Qaida in the Islamic Magreb (AQIM). The August attack was far more sophisticated than anything linked to Boko Haram before.Nigerian President Goodluck Jonathan calls the group a terrorist organization with global ambitions. In an interview in his presidential villa last week, Jonathan said there was "no doubt" Boko Haram has links with jihadist groups outside Nigeria. General Carter Ham, the head of the US military's Africa Command, said last year Boko Haram posed a threat to US and Western interests.At the same time, Boko Haram remains firmly focused on domestic Nigerian issues. When its secretive spokesman claims responsibility for attacks, he almost always lists local grievances that have little to do with the core ideologies of al-Qaida. The group's name means "Western education is sinful" in Hausa, the language spoken in northern Nigeria, the country's Muslim heartland. But its anger is directed not at America or Europe but at Nigeria's elites: at their perceived arrogance, their failure to deliver services, and the brutality of their security forces. Many Boko Haram members say their focus is on targeting officials who have locked up its members or misused state funds.Even Nigeria's national security adviser, General Owoye Azazi, who sees a link between Boko Haram and AQIM, urges caution in defining the group."We need to tackle Boko Haram from several perspectives," Azazi said in an interview. "If you go back to history, there are religious concerns, there are concerns about governance, and of course, political implications. It's a combination of so many things."