By Scott Malone and Samuel P. Jacobs
BOSTON/CAMBRIDGE, Massachusetts (Reuters) - Thousands of law enforcement agents from around the United States were to attend a memorial on Wednesday for a university police officer who authorities say was shot dead by the Boston Marathon bombing suspects, with Vice President Joe Biden to speak at the ceremony.
The service at the Massachusetts Institute of Technology honours Sean Collier, 26, who police say was killed by brothers Tamerlan and Dzhokhar Tsarnaev on campus on Thursday night. Tamerlan, 26, was killed in a separate shootout with police. Dzhokhar, 19, was captured and criminally charged from a hospital bed where he is recovering from gunshot wounds.
U.S. officials say the ethnic Chechen brothers planted and detonated two pressure-cooker bombs near the finish line of the Boston Marathon on April 15, killing three people and injuring 264. Ten people lost limbs in the bombing.
Attention has turned to whether U.S. security officials paid enough heed to Tamerlan Tsarnaev having been flagged as a possible Islamist radical by Russia. The FBI interviewed him in 2011 but did not find enough cause to continue investigating.
His name was listed on the U.S. government's highly classified central database of people it views as potential terrorists, sources close to the bombing investigation said. The list is vast, including about 500,000 people, which means that not everyone on the list is closely monitored.
Members of Congress briefed by law enforcement and media reports citing unidentified sources indicate Dzhokhar Tsarnaev has told investigators from his hospital bed that the brothers grew radical from anti-U.S. material on the internet and acted without assistance from any foreign or domestic militant groups.
"That basically seems to be the story, but I don't see how we can accept that," Representative Peter King, a New York Republican on House Homeland Security Committee, told CNN.
"It may end up being the truth, but here's a person who is a mass murderer, he's a person who can barely speak at all. I don't see why he would be giving up any accomplices he may have or talking about any connections his brother may have had in Chechnya or Russia," King said on Wednesday.
In an impromptu hearing on Monday before a federal magistrate judge in Beth Israel Deaconess Medical Center, Dzhokhar Tsarnaev was charged with two crimes that could result in the death penalty if he were convicted.
He is being represented by Miriam Conrad, the Boston area's top public defender, who has handled prior cases involving men accused of plotting to fly an explosive-laden remote-controlled plane into the Pentagon and helping to finance a 2010 planned car bomb attack in New York's Times Square.
MIT cancelled Wednesday's classes in Collier's honour. Authorities released videos and photos of the suspects, still unidentified at the time, on Thursday. Hours later, Collier, who had worked at MIT since January 2012, was shot and killed.
Collier and the youngest victim of the bombing attack, 8-year-old Martin Richard, were buried in private ceremonies on Tuesday.
Officials at the Cambridge mosque where Tamerlan Tsarnaev sometimes worshipped, and was known to have twice disrupted services, said on Tuesday they were unsure if they would offer burial services for him if asked by the family.
Investigators have focused on a trip to Dagestan last year by the older Tsarnaev and whether he became involved with or was influenced by Chechen separatists or Islamist extremists there.
A member of the extended family Tsarnaev said they were victims of a Russian plot to portray them as Chechen terrorists operating on U.S. soil.
The relative, Said Tsarnaev, who lives in Grozny, the capital of Russia's volatile Chechnya region, on Tuesday accused Moscow of sending false information to the United States to frame the suspects.
(Additional reporting by Mark Hosenball, Susan Cornwell and Patricia Zengerle in Washington; Editing by Daniel Trotta and Grant McCool)