* Trio took backpack, fireworks from dorm room-court papers
* Two Kazakhs charged with obstructing justice
* U.S. citizen charged with lying to investigators
* Men acted as FBI led hunt for suspects-court papers (Adds comments from suspects' attorneys)
By Scott Malone, Tim McLaughlin and Ross Kerber
BOSTON, May 1 U.S. authorities on Wednesday charged three men with interfering with the investigation of the Boston Marathon bombing, saying they hid fireworks and a backpack belonging to one of the suspected bombers as a manhunt was under way.
The three, two students from Kazakhstan and a U.S. citizen, were described as college friends of surviving bombing suspect Dzhokhar Tsarnaev, 19. They were not charged with direct involvement in the April 15 marathon bombings, which killed three people and injured 264.
But three days after the blasts, the trio moved swiftly to cover up for their friend when the FBI released pictures of the suspected bombers, made a public plea for help locating them and conducted a day-long manhunt that left much of Boston on lockdown, according to court papers.
Authorities charged the two Kazakhs, Azamat Tazhayakov and Dias Kadyrbayev, both 19, with conspiring to obstruct justice by disposing of a backpack containing fireworks they found in Tsarnaev's dorm room. The third man, Robel Phillipos, also 19, was charged with making false statements to investigators.
In their initial court appearances on Wednesday, none of the three entered a plea. After the proceeding, an attorney for Kadyrbayev denied wrongdoing.
"Dias Kadyrbayev absolutely denies the charges," said attorney Robert Stahl. "He did not know that this individual was involved in the bombing. His first inkling came much later."
Tsarnaev, who attended the University of Massachusetts at Dartmouth, is being held at a prison hospital where he is recovering from wounds sustained in a gun battle with police. His older brother, Tamerlan, died in the gunfight.
Kadyrbayev and Tazhayakov face up to five years in prison and Phillipos faces a maximum sentence of eight years.
Kadyrbayev, Tazhayakov and Phillipos were placed in the custody of U.S. Marshals after prosecutor Stephanie Siegmann argued that all three presented a "serious risk of flight."
None of the suspects addressed the court, other than to respond to the judge's questions. U.S. Magistrate Judge Marianne Bowler reprimanded Phillipos for not seeming to pay attention to the proceedings.
"I suggest you pay attention to me rather than looking down," Bowler said.
The three suspects' attorneys said their clients were shocked by the attacks.
"My client, Azamat Tazhayakov, feels horrible and was shocked to hear that someone that he knew ... at the University of Massachusetts at Dartmouth was involved with the Boston Marathon bombing," attorney Harlan Protass said.
Phillipos' attorney, Derege Demissie, said that his client had not assisted Dzhokhar Tsarnaev. As to the charge of making false statements, he said, "We look forward to litigating that in court."
Kadyrbayev and Tazhayakov had entered the United States on student visas and lived in New Bedford, Massachusetts, according to the court papers. Phillipos is a resident of Cambridge, Massachusetts.
A month prior to the bombings, Dzhokhar Tsarnaev told Kadyrbayev and Tazhayakov over a meal that he knew how make a bomb, Tazhayakov told the FBI, according to the documents.
On April 18, three days after the bombings, authorities released pictures of two men they identified as the suspects in the attack. Investigators at the time said they did not know the suspects' names and called on the public for help in identifying them.
Dzhokhar's three classmates quickly figured out their friend was one of the suspects, according to court papers. After seeing Tsarnaev's photo in TV news reports, Kadyrbayev texted him to say that he resembled the suspect, according to the complaint.
Tsarnaev's response included the phrase "lol" and "you better not text me," as well as "come to my room and take whatever you want," according to the court papers.
The three went to his dorm room that night and found a roommate who said that Dzhokhar had left.
The trio spent some time watching movies and then discovered an emptied-out fireworks tube, according to court papers. That discovery scared Tazhayakov, who then began to believe that Tsarnaev was involved in the bombing, according to court papers.
They decided to remove the backpack, fireworks and a laptop to help their friend "avoid trouble," according to court papers.
Tazhayakov is currently enrolled at UMass Dartmouth but has been suspended, the university said on Wednesday. Kadyrbayev and Phillipos are not currently enrolled in the school.
After waking up the next morning to learn that police were hunting for Dzhokhar Tsarnaev and that his brother, Tamerlan, was dead, Kadyrbayev decided to throw away the backpack with the fireworks tubes inside, according to court papers. He put the backpack and fireworks in a dumpster near his apartment.
Kadyrbayev and Tazhayakov were arrested on immigration violations on April 20.
Investigators recovered the backpack on April 26 in a New Bedford landfill. In addition to the fireworks, it included a homework assignment sheet from a class that Dzhokhar Tsarnaev was enrolled in.
In his first three interviews with police, Phillipos denied having gone to Tsarnaev's room on April 18, but in a fourth interrogation, on April 26, he confessed to the visit, the court documents said.
Dzhokhar Tsarnaev faces the possibility of execution if he is convicted of setting off the homemade pressure-cooker bombs in a crowd of tens of thousands of spectators at one of Boston's best-attended sporting events. (Additional reporting by Svea Herbst-Bayliss and Aaron Pressman in Boston and Mark Hosenball in Washington; Editing by Grant McCool and Jim Loney)