The brothers suspected of planting deadly bombs at the Boston Marathon may have gotten their ideas -- and even instructions on how to make explosives from household items -- from an English-language online magazine that Al Qaeda uses to radicalize and recruit Westerners.
A U.S. official told Fox News that Tamerlan Tsarnaev, 26, and his brother, Dzhokhar Tsarnaev, 19, built the bombs with instructions from Inspire magazine -- an English-language online magazine published by Al Qaeda in the Arabian Peninsula.
The publication is believed to have been started by Samir Khan, a U.S. citizen who moved in 2009 from his family's home in North Carolina to Yemen, where he was later killed in a U.S. drone strike along with Al Qaeda leader Anwar al-Awlaki. The magazine includes articles penned by Khan and others, like "Make a Bomb in the Kitchen of Your Mom."
The magazine is released through online jihadist forums -- some of which are open, while others are password protected, according to terrorism researchers. But one issue of Inspire encourages readers to seek out its information from non-jihadist websites, like blogs and even news outlets -- which publish the magazine's content -- so as not to attract the attention of law enforcement monitoring the forums, a counter-terrorism source told FoxNews.com.
In a 2010 edition of the magazine obtained by FoxNews.com, Al Qaeda warns Western readers to access information from non-Islamic websites.
"Whenever possible, try to get the information you need from websites that are non-Islamic or are not related to jihad. For example, you may visit sites that report on the mujahidin and cover their material such as SITE intelligence group or Memri," reads an article titled, "Tips for Our Brothers in the United States of America."
Mark Bederow, a New York-based criminal defense attorney, said simply accessing pro-Al Qaeda websites or publications is not enough for arrest. But he conceded that monitoring a website's traffic could be a valuable tool for law enforcement agents seeking to protect the public from terror plots. "The more we are learning about the Tsarnaev brothers, the more it seems the warning signs were there to consider them potentially very dangerous individuals," Bederow told FoxNews.com.
"Because of the First Amendment, we punish actions, not thoughts, however reprehensible they may be," he said. "Accessing a distasteful website and publicly sharing anti-American views, short of encouraging imminent illegal action, is not enough for arrest in this country."
Investigators say a radical brand of Islam appears to have motivated the two brothers suspected of bombing the Boston Marathon, but say they have found no indication the brothers were associated with any terrorist groups. The older brother was the driving force behind the attack, a source close to the investigation told Fox News.
Dzhokhar Tsarnaev was charged Monday in his hospital room, where he has been upgraded from "serious" to "fair" condition with a gunshot wound to the throat and other injuries suffered during his attempted getaway. His older brother, Tamerlan, died Friday after a fierce gun battle with police.
After interrogating Dzhokhar Tsarnaev since his capture on Friday, U.S. officials believe the brothers were motivated by their faith, apparently an anti-American, radical version of Islam. Another official called the Boston bombing suspects aspiring jihadists. All three officials spoke on condition of anonymity because they were not authorized to discuss the investigation publicly.
Dzhokhar Tsarnaev was charged with using and conspiring to use a weapon of mass destruction. He was accused of joining with his brother in setting off the shrapnel-packed pressure-cooker bombs that killed three people and wounded nearly 200 a week ago.
The brothers, ethnic Chechens from Russia who had been living in the U.S. for about a decade, practiced Islam.
Dzhokhar communicated with his interrogators in writing, precluding the type of back-and-forth exchanges often crucial to establishing key facts, said the officials, who spoke on condition of anonymity because they were not authorized to discuss the investigation publicly.
They cautioned that they were still trying to verify what they were told by Tsarnaev and were looking at such things as his telephone and online communications and his associations with others.
The disparity between the brothers' struggle to assimilate in the U.S. and their alleged bombing of the Boston Marathon reflects what counter-terror experts describe as a classic pattern of young first- or second-generation immigrants striking out after struggling to fit in.
The U.S. has long been worried about people in America who are not tied to any designated terrorist group but who are motivated by ideologies that lead them to commit violent acts. Some are motivated by radical religious interpretations; others feel ostracized by their communities.
On the Russian social networking site Vkontakte, Dzhokhar Tsarnaev described his world view as "Islam," but his personal goals as "career and money" -- a far more capitalistic goal than Muslim teachings that wealth ultimately belongs to God.
"There's a sort of weird identity crisis," said Kamran Bokhari, a Toronto-based expert on jihadism and radicalization for the global intelligence company Stratfor tells The Associated Press. "In many ways, these people are radicalized of extreme religious persuasions in the West that's not even reflective of what's back home. So they're sort of frozen in time, where they're rejecting the reality in front of them."
The brothers emigrated in 2002 or 2003 from Dagestan, a Russian republic that has become an epicenter of the Islamic insurgency that spilled over from the region of Chechnya.
It's still not clear what investigators believe motivated Tamerlan and Dzhokhar to attack. FBI agents interviewed Dzhokhar and got enough details to make "a strong case" against him, a U.S. intelligence official said.
Dzhokhar Tsarnaev had gunshot wounds to the head, neck, legs and hands when he was captured hiding out in a boat in a backyard in the Boston suburb of Watertown, authorities said.
A probable cause hearing -- at which prosecutors will spell out the basics of their case -- was set for May 30. According to a clerk's notes of Monday's proceedings in the hospital, U.S. Magistrate Judge Marianne Bowler indicated she was satisfied that Tsarnaev was "alert and able to respond to the charges."
Tsarnaev did not speak during the proceeding, except to answer "no" when he was asked if he could afford his own lawyer, according to the notes. He nodded when asked if he was able to answer some questions and whether he understood his rights as explained to him by the judge.
Federal Public Defender Miriam Conrad, whose office has been assigned to represent Tsarnaev, declined to comment.
The cases of homegrown and first-generation terror suspects in the U.S. are few, but the U.S. intelligence community has long been concerned about such potential attackers, particularly the threat posed by people like the Tsarnaev brothers who have no formal terror ties.
"And what makes them especially worrisome is that they're really difficult for us to detect and, therefore, to disrupt," Matt Olsen, director of the National Counterterrorism Center, said in June 2011 about homegrown violent extremists.
Last year, 14 Muslim-Americans were indicted for violent terror plots, down from 21 in 2011. The numbers peaked at a decade-high in 2009, when 50 Muslim-Americans were indicted, according to a February 2013 study on terror rates by University of North Carolina professor Charles Kurzman.
The U.S. intelligence director's office has declined to provide official government data on homegrown terrorists, or comment on the Tsarnaev brothers and the investigation into the bombings.
Fox News' Cristina Corbin, Mike Levine and The Associated Press contributed to this report.