Federal authorities arrested three friends of Boston Marathon bombing suspect Dzhokhar Tsarnaev Wednesday, accusing them of trying to obstruct justice by hiding evidence in the case and lying about it.

Azamat Tazhayakov and Dias Kadyrbayev, both Kazakh nationals who attended the University of Massachusetts at Dartmouth with Tsarnaev, were charged with "conspiracy to obstruct justice" for allegedly getting rid of a laptop computer and a backpack belonging to the suspected bomber. Their classmate, Robel Phillipos, a U.S. citizen from Cambridge, Mass., who reportedly knew Tsarnaev from high school, was charged with lying to federal officials during the bombing investigation.

Tazhayakov and Kadyrbayev appeared in federal court Wednesday where they were ordered held without bail. They are scheduled to appear in court again on May 14. One of their attorneys, Robert Stahl, said the men plan to plead "not guilty" to the charges. Phillipos, arrested Wednesday, appeared in federal court separately. There, a judge ordered him held without bail because he's a "flight risk." He's scheduled to appear before a judge again on Monday.

According to federal court documents, the three men, all 19, were close friends of Tsarnaev's, and at least one hung out with the suspected bomber after the April 15 attack. When the FBI released photos of the bombing suspects on April 18, Phillipos texted Kadyrbayev to say that one of the suspects looked like Tsarnaev. According to the filing, Kadyrbayev saw the photo and then texted Tsarnaev to tell him the same thing.

"LOL," Tsarnaev replied, according to the filing. The suspected bomber told his friend to "come to my room and take whatever you want"—though Kadyrbayev told federal authorities he regarded that comment as a joke.

But Tazhayakov told investigators that upon seeing those texts, he believed he would never see Tsarnaev alive again.

Later that night, Kadyrbayev and Tazhayakov, who shared an apartment off campus, met Phillipos at Tsarnaev's dorm room, where they spied a backpack containing fireworks that were "opened and emptied of powder" and other possible bomb-making components, according to court filings. Kadyrbayev allegedly told officials he knew at that moment that Tsarnaev was involved in the bombings, but instead of alerting police, he decided to remove the backpack and Tsarnaev's laptop from the dorm to help his friend "avoid trouble."

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The three stayed up all night watching bombing coverage, and amid reports that Tsarnaev was on the run, Kadyrbaev says they collectively decided to throw the backpack and laptop in a trash bin near the apartment he shared with Tazhayakov in New Bedford, according to the court filings. But Phillipos offered up a slightly different story, telling authorities he could not understand the "majority" of what his friends were saying because they were speaking in Russian. When asked by Kadrybaev what he thought he should do with Tsarnaev's items, Phillipos says he replied, "Do what you have to do."

Federal investigators interviewed Tazhayakov and Kadyrbayev on April 19 and, on April 20, they were detained on civil immigration violations. They have been in federal custody since then. The two appeared in immigration court Wednesday morning. Court filings suggest the two came clean early on about their efforts to conceal evidence related to Tsarnaev's alleged role in the bombings.

But federal officials have charged Phillipos with repeatedly lying to investigators about his role—insisting again and again that he didn't remember going to Tsarnaev's dorm room or removing possible evidence. But during his fourth interview on April 26, Phillipos allegedly admitted he had lied to federal agents and signed a confession detailing his role in the cover-up.

On April 26, federal investigators found Tzarnaev's backpack at a nearby landfill, according to court documents. It's unclear if the his laptop has been recovered.

If convicted, the three could each face as much as $250,000 in fines. Tazhayakov and Kadyrbayev also face a maximum sentence of five years in prison apiece, while Phillipos faces as much as eight years in prison. After the hearing, their attorneys strongly denied the charges made against their clients.

Stahl, who is Kadyrbayev's attorney but is also working closely with Tazhayakov since the two were charged jointly, said the men were "shocked and horrified" by the Boston attacks and by the knowledge that they knew the suspected bomber. He declined to specifically rebut the allegations laid out by federal officials Wednesday, but insisted the men had been cooperative with federal authorities and were stunned by the new charges.

An attorney for Phillipos, who declined to give his name, also denied the charges against his client in a press conference after the hearing--though he declined to elaborate. He suggested "the truth" would come out in court.

Tsarnaev, a 19-year-old college student, is charged with killing three and injuring more than 200 in the two bombs last month. He is in custody at a federal prison medical facility at Fort Devens, 40 miles outside of Boston, where he's being treated for injuries incurred in a shootout with police before his arrest. His older brother and suspected co-bomber, Tamerlan Tsarnaev, was killed while fleeing arrest.

In a statement, the Boston Police Department said there was no threat to public safety at this time.