BOSTON (AP) — The 19-year-old charged with the Boston Marathon bombing, his throat injured by a gunshot wound, wrote down answers to the questions of investigators about his motives and connections to any terror networks.

Dzhokhar Tsarnaev's answers led them to believe he and his brother were motivated by a radical brand of Islam without major terror connections, said U.S. officials, who spoke on condition of anonymity because they were not authorized to discuss the investigation publicly.

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But the written communication precluded back-and-forth exchanges often crucial to establishing key facts and meaning, said officials who cautioned they were still trying to verify what Tsarnaev told them and were poring over his telephone and online communications.

Tsarnaev was interrogated and charged Monday in his hospital room, where he was in serious condition with the throat wound and other injuries suffered during his attempted getaway. His brother, Tamerlan, 26, died Friday after a fierce gunbattle with police.

The charges came just hours before a memorial service for one of the three people killed in the bombings, 23-year-old Boston University graduate student Lu Lingzi, was held at the school and attended by hundreds of people, including Massachusetts Gov. Deval Patrick.

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"She's gone but our memories of her are very much alive," said her father, Lu Jun, who spoke in his native tongue and was followed by an English interpreter. "An ancient Chinese saying says every child is actually a little Buddha that helps their parents mature and grow up."

Tsarnaev, a student at the University of Massachusetts at Dartmouth, 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 Lu and two other people and wounded more than 200 on April 15.

The next step in the legal process against Tsarnaev is likely to be an indictment, in which federal prosecutors could add new charges. State prosecutors have said they expect to charge Tsarnaev separately in the killing of a Massachusetts Institute of Technology police officer who was shot in his cruiser Thursday night on the campus in Cambridge.

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After Tsarnaev is indicted in the bombing, he will have an arraignment in federal court, when he will be asked to enter a plea.

Under federal law, as a defendant charged with a crime that carries a potential death penalty, he is entitled to at least one lawyer who is knowledgeable about the law in capital cases. Federal Public Defender Miriam Conrad, whose office has been asked to represent Tsarnaev, filed a motion Monday asking that two death penalty lawyers be appointed to represent Tsarnaev, "given the magnitude of this case."

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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 Monday's 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.

Conrad declined to comment when contacted by The Associated Press.

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The criminal complaint outlining the allegations shed no light on the motive for the attack. The two U.S. officials who spoke anonymously said preliminary evidence from the interrogation suggests the brothers were motivated by religious extremism but were apparently not involved with Islamic terrorist organizations.

The brothers, ethnic Chechens from Russia who had been living in the U.S. for about a decade, practiced Islam.

A statement released Monday by Kazakhstan's Ministry of Foreign Affairs bolstered the U.S. officials' comments about seeking details on the suspect's other modes of communication and his associations.

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Two foreign nationals arrested Saturday on immigration violations are from the central Asian nation and may have known the suspects, the ministry said. U.S. authorities came across the students while searching for "possible links and contacts," it said.

Officials have not disclosed the names of the nationals, who the ministry said were found to have "violated the U.S. visa regime."

In the criminal complaint against Tsarnaev, investigators said he and his brother each placed a knapsack containing a bomb in the crowd near the finish line of the 26.2-mile race. The FBI said surveillance-camera footage showed Dzhokhar manipulating his cellphone and lifting it to his ear just instants before the two blasts.

After the first blast, a block away from Dzhokhar, "virtually every head turns to the east ... and stares in that direction in apparent bewilderment and alarm," the complaint says. Dzhokhar Tsarnaev, "virtually alone of the individuals in front of the restaurant, appears calm."

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He then quickly walked away, leaving a knapsack on the ground; about 10 seconds later, a bomb blew up at the spot where he had been standing, the FBI said.

The FBI did not say whether he was using his cellphone to detonate one or both of the bombs or whether he was talking to someone.

Among the details in the affidavit:

— 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.

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— One of the brothers — it wasn't clear which one — told a carjacking victim during their getaway attempt, "Did you hear about the Boston explosion? I did that."

— The FBI said it searched Tsarnaev's dorm room at the University of Massachusetts-Dartmouth on Sunday and found BBs as well as a white hat and dark jacket that look like those worn by one of the suspected bombers in the surveillance photos the FBI released a few days after the attack.

Shortly after the charges were unveiled, Boston-area residents and many of their well-wishers — including President Barack Obama at the White House — observed a moment of silence at 2:49 p.m. — the moment a week earlier when the bombs exploded.

In addition to that and the memorial for Lu, who was from Shenyang, China, and studied statistics at BU, a funeral was held Monday at St. Joseph Church for another victim, Krystle Campbell, a 29-year-old restaurant manager who had gone to watch a friend finish the race. Services have not been announced for the third bombing victim, 8-year-old Martin Richard, of Boston.

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As of Monday, 51 people remained hospitalized, three of them in critical condition. At least 14 people lost all or part of a limb; three of them lost more than one.