7 major new revelations about the Boston Marathon attacks

While surviving Boston bombing suspect Dzhokhar Tsarnaev remains hospitalized with wounds sustained during his flight from police, investigators are beginning to probe deeper into the case for more information and a motive. In preliminary interviews conducted at Beth Israel Deaconess Medical Center in Boston, Tsarnaev reportedly began filling in the blanks.

Here are the latest updates in the case:

1. Dzhokhar may have confessed

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Multiple media outlets reported Tuesday that Tsarnaev has confessed that he and his elder brother Tamerlan carried out the attack. The New York Times, The Boston Globe, and The Washington Post, all citing anonymous officials involved in the case, said Dzhokhar admitted his guilt by writing responses to investigators' questions. Dzhokhar has a gunshot wound to his neck, among other injuries, and is barely able to speak.

So far, no government or law enforcement official has publicly corroborated that claim. And it should be noted that the investigation is still in its early stages, which means the reported admission, if it indeed took place, would still need to be checked out by law enforcement.

2. They likely acted alone

Authorities now believe that the brothers acted alone, with no support from a domestic or foreign terror group. Rather, officials believe the two were "self-radicalized."

From The Washington Post's Scott Wilson, Greg Miller, and Sari Horwitz:

Officials have said before that they suspected that the plot did not stretch beyond the two suspects, and Dzhokhar's admission of guilt lends more weight to that theory. If the two did in fact act alone, that should end the debate about whether he could be tried as an enemy combatant.

3. Suspect cites Islam, U.S. wars as motive

Though the suspects are believed to have acted independently, they were allegedly influenced by radical Islamic teachings, and saw the attack as payback for the American-led wars in Iraq and Afghanistan. According to CNN and NPR, Dzhokhar has said Tamerlan was the "driving force" behind the attack.

From CNN's Jake Tapper:

According to Fox News, the two suspects are believed to have found instructions for their bombs from the English-language al Qaeda magazine Inspire. However, other government officials have cautioned that the brothers may have found that information elsewhere online.

Meanwhile, The Associated Press is reporting that Tamerlan may have also been exposed to radical teachings by a friend who was a Muslim convert.

From the AP:

4. Fireworks purchased before attack

Tamerlan purchased a load of fireworks two months ago from a chain store in New Hampshire, according to the store's vice president. Firework sales are illegal in Massachusetts, so state residents often hop across the border to pick up the contraband there.

"He came in and he asked the question that 90 percent of males ask when they walk into a fireworks store: 'What's the most powerful thing you've got?'" Phantom Fireworks Vice President William Weimer told The New York Times.

It's unclear if the brothers used powder from those fireworks — two large mortar kits with 24 shells apiece — in any of the weapons used in the Boston attack. Weimer told the Times that he didn't think the suspects purchased enough fireworks to obtain the powder necessary to create all the bombs used in the Boston attack and the ensuing police chase.

An affidavit submitted with the criminal complaint against Dzhokhar notes that police found a "large pyrotechnic" in his dorm room.

5. Tamerlan had a criminal past

Massachusetts police are investigating whether Tamerlan is responsible for a September 2011 triple-homicide in Waltham, Mass., a town just outside Boston. One of the victims in that unsolved case is a former roommate of Tamerlan's, though investigators have not said if there is any new information that prompted them to probe that potential link, other than the Marathon bombings.

And according to The Washington Post, Tamerlan was arrested in 2009 for a domestic dispute in which he allegedly slapped his girlfriend. He was charged with assault and battery, and the case was dismissed six months later.

6. FBI says it had no legal authority to flag Tamerlan

The FBI claims that, despite a debate over whether the agency missed a chance to flag the elder Tsarnaev two years ago, the agency had no legal authority to do so. Previous reports noted that Russia had specifically asked the U.S. for information on Tamerlan when he traveled there in 2011. Speculation swirled that a typo or agency malfeasance led to Tamerlan going by unnoticed, but the FBI shot those theories down.

According to the FBI, agents performed an initial investigation at Russia's behest, but when they asked if they should delve deeper, they got no response. In the end, the agency interviewed Tamerlan and his family on its own, determining that they did not pose a terror threat.

7. Injury tally rises

While the number of deaths related to the marathon bombing has stood at three since last Monday, the injury tally has steadily risen since then. Though initially estimated at around 160, that total has climbed to more than 260 as more people have checked themselves in for treatment over the past week.

"We have seen a steady increase in the number of patients," Nick Martin, a Boston Public Health Commission spokesman said Tuesday. "An example is people with hearing problems who might have initially assumed it was a temporary issue. But it lasted longer than they thought it would."