One of them later threw the backpack in the garbage, and it wound up in a landfill, where it was discovered by law enforcement officers last week, authorities said. In the backpack were fireworks that had been emptied of their gunpowder.
Investigators have not said whether the pressure cooker bombs used in the attacks were made with gunpowder extracted from fireworks.
The lawyers for the Kazakh students said their clients had nothing to do with the bombing and were just as shocked by the crime as everyone else. Phillipos' attorney, Derege Demissie, said outside court: "The only allegation is he made a misrepresentation."
The Kazakh students did not request bail at a court hearing and will be held for another hearing May 14. Phillipos was held for a hearing on Monday. If convicted, Kadyrbayev and Tazhayakov could get up to five years in prison and a $250,000 fine. Phillipos faces a maximum of eight years behind bars and a $250,000 fine.
The mother of the Tsarnaev brothers has said the allegations against her sons are lies.
Kadyrbayev and Tazhayakov have been in jail for more than a week on allegations they were in violation of their student visas, one because he was skipping classes, the other because he was no longer enrolled.
Tazhayakov was allowed to return to the U.S. from Kazakhstan in January despite not having a valid student visa, a federal law enforcement official told The Associated Press. His student visa status had been terminated because he was academically dismissed from the university, said the official, who was not authorized to discuss the case and spoke on condition of anonymity.
All three men charged Wednesday began attending UMass with Tsarnaev in 2011, according to the FBI.
Kadyrbayev, an engineering major, said he and Tazhayakov hung out with Tsarnaev on and off campus. The three often spoke Russian among themselves.