They had traced a mobile phone linked to suspected bomber Dzhokhar Tsarnaev to the New Bedford, Massachusetts, apartment rented by two Kazakh nationals who were students at the University of Massachusetts at Dartmouth.
The two, Dias Kadyrbayev and Azamat Tazhayakov along with Kadyrbayev's girlfriend, came out with their hands up and quickly came face-to-face with FBI special agent John Walker, who interviewed the three separately.
"I told them, Dzhokhar Tsarnaev, effectively he's dead. Whether he's still living or is going to go away, his life is over. Your life is not over," Walker said at a pretrial hearing for the two Kazakh exchange students and Cambridge, Massachusetts, resident Robel Phillipos.
All three have been charged with interfering with the investigation into the blast that killed three people and injured 264.
Federal prosecutors contend that three men went to Tsarnaev's dorm room at the University of Massachusetts at Dartmouth three days after the attack and removed a backpack and laptop computer as police searched for the suspected bomber.
After interviewing the three people found at the apartment, Walker said he asked them to submit to further questioning at a nearby state police barracks.
Walker spoke at the first day of a hearing where Kadyrbayev is also expected to take the stand as his lawyers ask U.S. District Judge Douglas Woodlock not to allow statements made to police at that time to be heard at his upcoming trial.
On the day Tazhaykov and Kadyrbayev were arrested, initially on immigration violations, Walker said they told him the backpack had been thrown into a dumpster outside their apartment building and that they had seen it hauled away.
Kadyrbayev and Tazhayakov face charges of conspiracy and obstruction of justice, which carry a penalty of up to 25 years in prison, while Phillipos faces a less serious charge of lying to investigators, which carries a possible 16-year sentence.
Attorneys for Tazhayakov and Phillipos, who were also present in court, said their clients would not be taking the stand.
Woodlock denied a request on Tuesday to move the trials of the three outside of Massachusetts.
Woodlock agreed to requests by the defendants to grant each his own trial rather than to try them together, however.
Kadyrbayev's trial was set to begin June 30, with Tazhayakov's and Phillipos' to follow in September.
Prosecutors said each of the trials should take about two weeks, meaning that all proceedings would be completed before the scheduled November start of Tsarnaev's trial.
Tsarnaev is being held at a prison west of Boston awaiting trial.
The Kazakhs, who have been held in federal custody on immigration violations since their arrest days after the attack, were allowed to appear in court in dress shirts and trousers, rather than prison jumpsuits. Phillipos, who is out on bail, arrived in a light gray business suit and tie.