Just over a month after Boston Marathon bombing suspect Tamerlan Tsarnaev was killed during a standoff with police, investigators said they have begun to piece together a picture of what he did during a six-month visit last year to Dagestan, a volatile region in southern Russia that is home to Tsarneav's parents as well as a violent struggle with Islamist insurgency.
American investigators believe Tsarnaev traveled to Dagestan seeking to make contact with militant groups, but for reasons that remain unclear, he was either unable or unwilling to join their ranks.
As they peel back the layers of the man accused of working with his younger brother to set off a pair of bombs near the finish line of the Boston Marathon April 15, investigators said they are finding a frustrated young man who felt out of place in the United States.
They said Tsarnaev appears to have been largely self-radicalized before arriving in Dagestan in search of a lifestyle that may not have met his expectations either, according to U.S. officials close to or briefed on the investigation. The officials spoke on the condition of anonymity.
The officials described Tsarnaev as a typical lone wolf.
While Tsarnaev's radicalization appears to have deepened during his time in Dagestan, investigators have not found a particular contact there or a "manifesto," on his computer or elsewhere that would explain why he and his younger brother Dzhokhar allegedly placed bombs at the finish line of the Boston Marathon, the officials said. Hours after Tamerlan was killed in the police shootout, Dzhokhar was apprehended and remains in custody.
While officials stressed the investigation is still ongoing, they have also found no signs that Tamerlan Tsarnaev was affiliated with an international terror organization like al Qaeda. Similarly, they have found no evidence to suggest he was directed to strike the U.S. by anyone he met in Dagestan. They have not found any signs of suspicious contacts during Tsarnaev's trips to visit his father's family in Chechnya, which has also battled an Islamist insurgency, and probes into Tsarnaev's father's rumored ties to Chechen security officials have also not revealed anything of concern, the officials said.
Tamerlan Associate Joined Militant in 'The Forest', But Not Tamerlan
Tsarnev's closest known militant contact in Dagestan appears to have been a young man named Mahmud Mansur Nidal, officials said. The two were often seen together leaving a Salafist mosque, popular with fighters, in Makhachkala.
But while Nidal eventually went off to join a militant group -- what locals call going "into the forest" -- investigators say they have uncovered no evidence that Tsarnaev joined him. Nidal would eventually be killed in a police raid after returning to visit family.
Tsarnaev had also been in touch over the internet with a Russian-Canadian convert to Islam and suspected militant named William Plotnikov, but officials say they have no evidence to suggest the two ever met in person. Contrary to previous reporting, investigators say they do not believe Tsarnaev dropped off the map after Plotnikov was killed by police in July, shortly before Tsarnaev left Russia to return to the United States.
Investigators have also taken a hard look at Magomed Kartashov, Tsarnaev's distant cousin and the founder and leader of a Islamist group called the Union of the Just. The group is anti-American and campaigns for the application of Sharia, or Islamic law.
The cousins met several times during Tsarnaev's stay in Dagestan. Kartashov's lawyer, Patimat Abdullaeva, told ABC News by phone that the two did discuss religion, but she insisted Tsarnaev was the one with extremist views. Kartashov is in prison for an unrelated matter -- waving an Islamist flag during a wedding procession -- but his lawyer says Russian investigators have interviewed him there about his interactions with Tsarnaev.
Magomed Magomedov, another member of Union for the Just, told ABC News he also saw Tsarnaev several times last year, at the mosque and around Makhachkala, but could not remember their discussions about religion. He described Tsarnaev as being aloof and out of place in Dagestan.
"He was sticking out, it was obvious he is not local. He liked to draw attention with his expensive and fancy clothes. His haircut was something no one has seen before," he said.
That description matches the picture that investigators are painting of Tsarnaev. They said when Tsarnaev arrived in Dagestan, his flashy appearance and demeanor immediately set him apart.
He also apparently drew attention to himself by claiming to know more about Islam than he really did. According to investigators, Tsarnaev would often recite things he had read or seen on the internet, often confusing those he was trying to impress.
"He was driving people crazy," one official said.
The officials said he was not as strict a practitioner of Islam as he claimed to be.
While his younger brother and alleged co-conspirator Dzhokhar has been described as the family pothead, one official said Tamerlan was also fond of marijuana, spending hours high on the couch in Massachusetts where he did not have a steady job.
The FBI has met with Tsarnaev's parents at least once. Officials said they are still planning to meet with nine or 10 other individuals, including with Tsarnaev's extended family, childhood friends, and contacts at the mosque. Those meetings were described as "tying up loose ends" rather than suspicious leads.
Amid Tensions, U.S.-Russia Play Nice on Boston Investigation
The American officials praised the unusual level of cooperation they've received from their Russian counterparts.
Often that relationship is plagued by lingering Cold War-era mistrust, but officials described how both sides have poured over linkage maps together, with the Russians sharing their knowledge and analysis, even suggesting individuals that the American side may want to interview. That, they say, is different from the past when the Russians offered little more than terse responses to American requests for information.
Indeed, that mistrust may have hindered early attempts to investigate Tsarnaev in 2011, when Russia asked the United States to look into what it suspected were Tsarnaev's plans to join extremist groups abroad. The FBI found nothing to support those claims, but said Russia did not follow up when the bureau asked for more information. That communication gap has become a target for a group of American lawmakers who plan to visit Russia next week to investigate the bombing.
"If there was a distrust, or lack of cooperation because of that distrust, between the Russian intelligence and the FBI, then that needs to be fixed and we will be talking about that," Rep. Dana Rohrabacher (R-Calif.), the chairman of the House Committee on Foreign Affairs' Subcommittee on Europe, Eurasia and Emerging Threats who is leading the Congressional delegation, told ABC News by telephone.
While the officials described their cooperation with the Russians as "unprecedented," they grumbled privately that they have been unable to do a methodical step-by-step investigation like they are used to doing in the U.S., or even in other countries where they have long-standing cooperation. American investigators from the FBI have been unable to travel to Dagestan without permission from the Russian authorities.
Still, they insist they have been able to confirm much of what they have been told by Russian government officials from what one official vaguely described as "other channels."
ABC News' Dada Jovanovic contributed to this report.