Suspect admits he and late brother carried out Boston bombings

The 19-year-old Dzhokhar, who remains hospitalized for wounds suffered in a shootout with police, also said that he and his brother killed an MIT campus police officer on Thursday night, according to the source, who spoke on condition of anonymity.

The surviving suspect made his statements Sunday at Beth Israel Deaconess Medical Center.

FBI agents initiated the questioning without reading Tsarnaev his Miranda rights, although doing so is not required under certain circumstances.

In addition to Dzhokhar's admission, authorities also have taken the testimony of a man the brothers carjacked before Tamerlan, 26, died early Friday morning in a shootout with police.

"We just killed a cop. We blew up the marathon. And now we're going to New York. Don't (expletive) with us," Tamerlan told the driver, according to police sources cited by the Globe.

A federal magistrate arraigned Dzhokhar on Monday at the hospital.

Tsarnaev was formally charged with using weapons of mass destruction against people in detonating two bombs on April 15 near the finish line of the Boston Marathon, killing three people and wounding more than 180 others.

The suspect, who remains in serious condition, is communicating with federal investigators in writing since he cannot speak because of a throat wound sustained in the shootout with police.

The two men had firearms, ammunition and more bombs in their possession, suggesting they planned more attacks, the FBI said.

Dzhokhar told investigators that he and Tamerlan did not have contact with terrorist groups and that they acted for religious reasons and out of anger over U.S. military operations in Muslim nations.