BOSTON (AP) — Tamerlan Tsarnaev, one of two brothers suspected in the Boston Marathon bombing on April 15, was an ardent reader of jihadist websites and extremist propaganda, U.S. officials said Tuesday, adding another piece to the body of evidence they say suggests he and his younger brother Dzhokar were motivated by an anti-American, radical version of Islam.

As he lay in his hospital bed with a gunshot wound to the throat, Dzhokhar Tsarnaev, 19, was charged on Monday with carrying out the bombing with his elder brother, who died last week in a gun battle. Tsarnaev could get the death penalty.

Interrogators questioned him at the hospital, letting him write down his replies, and his answers led them to believe the brothers were motivated by religious extremism but appeared to have no major terrorist group connections, said U.S. officials, who spoke on condition of anonymity because they were not authorized to discuss the investigation publicly.

However, the written communication precluded back-and-forth exchanges often crucial to establishing key facts, officials said. They warned that they were still trying to verify what Tsarnaev told them and were poring over his telephone and online communication.

On Tuesday, two officials said the elder brother frequently looked at extremist sites, including Inspire magazine, an English-language online publication produced by al-Qaida’s Yemen affiliate. The magazine has endorsed lone-wolf terror attacks.

Also Tuesday, family, friends and colleagues gathered to pay their final respects to Sean Collier, the Massachusetts Institute of Technology police officer who authorities say was ambushed and killed by the Boston Marathon bombing suspects.

Services were also held this week for the three victims of the bombing:  restaurant manager Krystle Campbell, 29; Chinese graduate student Lingzi Lu, 23; and Martin Richard, 8.

Some estimates put the number of people injured in the twin blasts caused,

investigators said, by bombs in pressure cookers, as high as 282; at least 51 remained in Boston area hospitals.

Dzhokhar Tsarnaev, whose condition was upgraded Tuesday from serious to fair, was charged with using and conspiring to use a weapon of mass destruction. The University of Massachusetts-Dartmouth student was accused of joining with his brother in setting off the bombs.

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

The next step in an apparently lengthy legal process against Tsarnaev is likely to be an indictment, to which federal prosecutors could add new charges.

State prosecutors have said they expect to charge Tsarnaev separately in the killing of the MIT officer.

Federal public defender Miriam Conrad, whose office has been asked to represent Tsarnaev, asked that two death penalty lawyers be appointed to represent Tsarnaev, “given the magnitude of this case.”

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.

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.

The criminal complaint outlining the allegations shed no light on the motive for the attack.

In the criminal complaint, investigators said the Tsarnaev brothers 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 moments 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. But Dzhokhar Tsarnaev, unlike practically everyone else around him, appeared calm, the FBI said.

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.