Did they act alone? How did they become radicalized? Those are the lingering questions surrounding Boston bombing suspects Tamerlan and Dzhokhar Tsarnaev, and investigators are zeroing in on their friends and associates for answers.
The role of these contacts is being constantly revised in the media, but here's what we know about them so far:
Dias Kadyrbayev, Azamat Tazhayakov, and Robel Phillipos
These three students were taken into custody today on separate charges involving their relationship with Dzhokhar Tsarnaev.
Kadyrbayev and Tazhayakov, both Kazakh nationals, are being charged with obstruction of justice for allegedly helping destroy evidence linking Dzhokhar to the Boston bombing. Officials tell CNN's Jake Tapper they do not know if the three were involved in the attack, but say the two Kazakhs disposed of Dzhokhar's fireworks, laptop computer, and backpack. Phillipos, a 19-year-old U.S. citizen, is being charged with making false statements to law enforcement officials during a terrorism investigation.
According to the affidavit supporting the criminal complaint, the three men all began attending the University of Massachusetts at Dartmouth at the same time in 2011 (Kadyrbayev and Tazhayakov entered the United States overstayed their student visas but still managed to fly under the radar of Customs and Homeland Security officials). The complaint alleges that Kadyrbayev and Tazhayakov saw TV reports identifying the Tsarnaev brothers as suspects in the bombing before they discarded the backpack and laptop. None of the men entered a plea at their initial court appearances, but a lawyer for Kadyrbayev denied the chages. "Dias Kadyrbayev absolutely denies the charges," attorney Robert Stahl said. "He did not know that this individuala was involved in the bombing. His first inkling came much later."
The source of Tamerlan Tsarnaev's radicalization has shifted significantly in recent days, with the latest suspect being a Canadian jihadist killed by Russian police last year after joining the Islamic insurgency in Dagestan. The scoop came from the respected Russian newspaper Novaya Gazeta and was fleshed out by the Associated Press yesterday.
Security officials suspected ties between Tsarnaev and the Canadian - an ethnic Russian named William Plotnikov....
The newspaper said the men had social networking ties that brought Tsarnaev to the attention of Russian security services for the first time in late 2010.
It certainly wouldn't be surprising if the men had met. Both were amateur boxers of roughly the same age whose families had moved from Russia to North America when they were teenagers. In recent years, both had turned to Islam and expressed radical beliefs. And both had traveled to Dagestan, a republic of some 3 million people.
In August, Plotnikov's father told the Canadian newspaper National Post that while his son converted to Islam in 2009, he only learned of his son's radicalization after receiving videos and photographs following his death. The footage shows William vowing to kill in the name of Allah and posing with an automatic rifle over his shoulder.
"Plotnikov had been detained in Dagestan in December 2010 on suspicion of having ties to the militants and during his interrogation was forced to hand over a list of social networking friends from the United States and Canada who like him had once lived in Russia," notes the AP. "Tsarnaev's name was on that list, bringing him for the first time to the attention of Russia's secret services."
After Plotnikov's death, Russian officials searched for Tsarnaev but lost track of him before he jumped on a plane to the United States.
Mahmoud Mansour Nidal
In today's Washington Post, U.S. officials tell the newspaper the FBI is investigating Mahmoud Mansour Nidal, a Palestinian and Kumyk man suspected of recruiting Islamic insurgents in Dagestan. Like Plotnikov, Nidal was also killed by Russian authorities last year. The Russian newspaper Novaya Gazeta reported that Tsarnaev was spotted with Nidal, "who was believed to have ties to Islamic militants in the southern Russian region." In May 2012, authorities killed Nidal after he refused to surrender to officials who had surrounded his house in Makhachkala.
Mikhail "Misha" Allakhverdov
Christian Caryl poured cold water on speculation that a mysterious Muslim convert named "Misha" had radicalized Tamerlan after interviewing Allakhverdov at his home in Rhode Island. Allakhverdov said he knew Tamerlan in Boston but had lost contact with him after moving away from the city three years ago. While he declined to describe the nature of his relationship with Tamerlan, he said he never met the extended Tsarnaev family, including Uncle Ruslan, who accused Allakhverdov of brainwashing Tamerlan. "I wasn't his teacher. If I had been his teacher, I would have made sure he never did anything like this," Allakhverdov said. Caryl's report seemed to confirm reports that the FBI has found no connection between Allakhverdov and the bomb plot.