His comments appear to support investigators' theory that the attack was hastily conceived by two siblings who were self-radicalized.
Writing answers from his hospital bed because he was shot in the throat, the 19-year-old accused bomber also said that his slain older brother, Tamerlan, was "upset" by the U.S. wars in Iraq and Afghanistan and that anger was the motivation to plant two crude homemade bombs along the crowded race route.
A U.S. counter-terrorism official said Dzhokhar Tsarnaev mentioned the wars "as a general justification for what he did," while a law enforcement official said he did not seem as bothered about America's role in the Muslim world. The law enforcement official said authorities were developing a clearer picture from the suspect's responses and from records of Internet activity that Tamerlan Tsarnaev was the driving force behind the April 15 bombings.
Fresh details about the grisly plot emerged on a grim, windswept day of funerals for 8-year-old Martin Richard, the youngest of the three people killed in the blasts, and for 26-year-old Sean Collier, a Massachusetts Institute of Technology security officer shot to death during the manhunt that ensued.
The Boston Public Health Commission said 264 runners and bystanders were treated for injuries related to the bombings, more than previously known, as people continued to trickle into emergency rooms. About 51 remain in the hospital.
A team of law enforcement and intelligence agents from the High-Value Detainee Interrogation Group questioned Tsarnaev before a federal magistrate opened a hearing at his bedside Monday and informed him of his his constitutional right to remain silent to avoid self-incrimination. He faces federal criminal charges of using a weapon of mass destruction, and if convicted could face the death penalty.
During the questioning before he was formally charged, Dzhokhar said he and his brother did not practice detonating the pressure cooker bombs, according to a U.S. official who has been briefed on the interrogation and who spoke on condition of anonymity because the investigation was ongoing.
Officials said no evidence had emerged to indicate the brothers had co-conspirators, and despite U.S. fears of foreign involvement, investigators have tentatively concluded that Tamerlan did not meet with Islamist militants or attend a training camp during a visit to Russia last year. That trip was his only known foreign travel as an adult.
A law enforcement official said investigators believe the Tsarnaevs built their bombs after consulting a how-to guide in Inspire, an online magazine published by the Qaida franchise in Yemen. In a 2010 article, the English-language magazine urged would-be terrorists to build a crude bomb using a pressure cooker, gunpowder from shotgun shells or fireworks, and other easily obtainable items.
Investigators say they have confirmed that Tamerlan Tsarnaev purchased fireworks in southern New Hampshire, just over the border from Massachusetts, earlier this spring. On Feb. 6, they say, he walked into the Phantom Fireworks store in Seabrook, N.H., and asked the clerk, "What is the most powerful item you have?"
The president of Phantom Fireworks, Bruce Zoldan, said in a telephone interview that the clerk behind the counter that day, Megan Kearns, told investigators that she remembered Tsarnaev because most customers buy an assortment of fireworks, but he only wanted the biggest sets they sold.
He paid more than $400 in cash for two "Lock and Load" reloadable mortar kits, each with four tubes and 24 shells, Zoldan said. Each shell can fly more than 100 feet into the air and explode in a colorful and noisy light display. The store records the name and driver's license number of each customer, Zoldan said. That was how the company linked the purchase to Tamerlan Tsarnaev after the FBI asked about the two brothers last Friday.
The shells Tsarnaev purchased would hold 1.5 pounds of gunpowder, but it's unclear whether the explosive was used in the marathon bombings.
"It certainly appears as if the bomb design is consistent with that described in Inspire, but there may be other online sources," said Rep. Adam B. Schiff, D-Calif., who attended a House briefing on the case. "Plainly, a significant part of the radicalization took place online."
Amid questions about whether U.S. intelligence or law enforcement agencies missed possible warning signs, Homeland Security Secretary Janet Napolitano appeared on Capitol Hill and defended her agency's handling of the case.
The FBI interviewed Tamerlan Tsarnaev at his home after Russian authorities warned in early 2011 that he might have ties to radical groups, and the FBI subsequently placed an immigration alert on his name.
He traveled to the Russian republic of Dagestan in early 2012, but the alert was not triggered because the airline misspelled his name on the manifest. By the time he returned six months later, the one-year FBI alert had expired and he was not flagged for additional screening, Napolitano said.
"By the time he returned, all investigations had been -- the matter had been closed," Napolitano told the Senate Judiciary Committee. She said she would provide additional details in a classified hearing later this week.
The FBI said last week it interviewed Tamerlan in early 2011 after Russian authorities warned that he might have connections to Islamist militant groups. The FBI found no such evidence and on Tuesday, they pointed fingers at Russian authorities for not answering their follow-up questions at the time.
"The Russians now are falling short on backing up their initial claims," about Tamerlan's alleged radical ties, a U.S. counter terrorism official said. "It's tenuous. They certainly didn't have much on him, or else why did they let him in the country, and why did they let him leave?"
Tamerlan, 26, died after a firefight with police on a Watertown street early last Friday. His younger brother was captured Friday night with gunshot wounds to the head, neck, legs and hand. Doctors at Beth Israel Deaconess Medical Center upgraded his condition from "serious" to "fair" on Tuesday.
An attorney for Tamerlan's widow, Katherine Russell, said she was "doing everything she can to assist with the investigation."
"The injuries and loss of life-to people who came to celebrate a race and a holiday-has caused profound distress and sorrow to Katie and her family. The reports of involvement by her husband and brother-in-law came as an absolute shock to them all," her attorney, Amato A. DeLuca, said in a written statement.
Boston Mayor Thomas Menino announced Tuesday that $20 million has been raised so far to help the wounded and the families of the dead, with donations ranging from a $1 million check from one contributor, to "young people doing lemonade stands, $5, $10, it runs the gamut."
In all, One Fund Boston has received 50,000 donations from around the world, he said.
"I never imagined after this tragedy last Monday the generosity of the folks," said an emotional Menino. "The business community of Boston especially, but around the world.... Five million dollars was generated by simple clicks of your computer."
Kenneth Feinberg, who administered victims' funds after the terrorist attacks of Sept. 11, 2001, and other disasters, will oversee disbursement of the money. On Tuesday, he said the deadline for applications is June 15, and checks will be cut to the victims and their families by June 30.
"I am amazed, in my experience, to see this type of outpouring so quickly in such large amounts after this horrific tragedy," Feinberg said. "One thing I've learned is ... never underestimate the charitable impulse of the American people."
Boston officials also partly reopened Boylston Street for the first time since the bombings turned the thoroughfare into a police crime scene. Traffic and pedestrians were still barred, but people who live or work along the usually-busy street were instructed to meet at Hynes Convention Center at designated times, and then were escorted to their buildings.
Everyone was told to leave by 7 p.m., however, and it wasn't clear when the street will reopen to normal traffic.
Walking past the bomb sites on Boylston is "very eerie," said Tim Donohue, vice president with IHRDC, a company that provides training for the oil and gas industry. He said it has been difficult "not knowing each day whether we're going to be allowed back to our offices."
Enrique Rivera, a cook at Lolita's Cocina and Tequila Bar, said the lost week of work could mean a dent in his income. "If we don't work, we don't earn," said Rivera, who is from Mexico.
Rivera spent several hours helping clean the restaurant, but said he did not know when they could re-open. "They won't allow in everything we need to run the restaurant," he said. "For example, the trucks that bring in meat, vegetables-we don't have those."
At a late afternoon news conference, Boston police superintendent William Evans gave an updated version of Dzhokhar's arrest Friday night, saying the suspect fired first as police approached his hiding place in a motorboat stored behind a home in Watertown.
"Shots rang out behind the house," he said. He said the suspect was "poking, poking, poking" at the plastic tarp over the boat to peer outside or to fire more shots.
He said police "took cover" in the driveway and in two adjacent homes. "We hoped to negotiate him out," Evans said.
"We were driven by the tragedy. We all were...We had a mission. We wanted to catch this guy. Not only for what they did to our poor victims, but for what they did to our marathon."
In the end, Dzhokhar climbed out of the boat and the FBI let Massachusetts Bay Transport Authority police put handcuffs on him, in respect for one of their officers who was wounded the night before.
When it was over, "there was no greater feeling in the world," Evans said. "We all started hugging each other."
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