BOSTON (TIP): A friend of the accused Boston Marathon bomber grew suspicious that Dzhokhar Tsarnaev had carried out the attack when he threw away a backpack and laptop he had removed from the suspect’s dorm room, a federal agent testified on May 15.

Three of Tsarnaev’s college friends face charges of hampering the probe into the blast, which killed three people and injured more than 260. At hearings this week, lawyers for one student, Dias Kadyrbayev, sought to prove that the statements he made to law enforcement four days after the bombing were not voluntary and should not be admitted at trial.

James Wiroll, a special agent with the US department of homeland security, recalled arresting Kadyrbayev and his roommate Azamat Tazhayakov, both Kazakh nationals, on immigration violations five days after the attack. Wiroll said Kadyrbayev told him he had thrown away the backpack, which contained empty fireworks cases, and a laptop, after coming to suspect that Tsarnaev had committed the bombing.

“He suspected Tsarnaev was one of the Boston Marathon bombers and he threw the items away,” Wiroll said, reading from a report written shortly after the arrest. Prosecutors on Thursday released some 300 text messages that were sent or received by Kadyrbayev, including a series of messages from April 18 — shortly after the FBI released photos of the Tsarnaev brothers, the Boston Globe reported. In one message, Kadyrbayev writes to Tsarnaev: “u saw the news?” Tsarnaev responds: “Better not text me my friend,” adding, “Lol,” according to the report.

“If yu want yu can go to my room and take what’s there,” Tsarnaev then wrote. Later that night, Kadyrbayev found Tsarnaev’s backpack, according to the indictment. Tsarnaev is awaiting trial. His older brother, Tamerlan, died in a gunbattle with police four days after the attack. A diplomatic representative from Kazakhstan was present and translated some documents when Wiroll interviewed Kadyrbayev. Kadyrbayev and Tazhayakov were first questioned by investigators four days after the bombing when heavily armed law enforcement agents arrived at their New Bedford, Massachusetts, apartment.

The next day, they were arrested on charges of violating the terms of their student visas. A stream of federal agents had testified at three days of pre-trial hearings that Kadyrbayev’s interviews were voluntary. “He was relaxed, he was animated when he spoke, at times he would laugh,” said FBI special agent Steven Schiliro, who interviewed Kadyrbayev the night before his arrest.

Kadyrbayev and Tazhayakov face conspiracy and obstruction of justice charges, which carry a penalty of up to 25 years in prison, while a third man, Robel Phillipos of Cambridge, Massachusetts, faces a less serious charge of lying to investigators, which could mean a possible 16-year sentence.