Boston Marathon Bombing suspect Dzhokar Tsarnaev.
Boston Marathon Bombing suspect Dzhokar Tsarnaev.Reuters

The teen suspect in the Boston Marathon bombings, Dzhokar Tsarnaev, told investigators that his elder brother, another suspect, had masterminded the 15 April attack, a US government source said on Monday.

The source also revealed that the 19-year-old, who lies in the intensive care unit of Boston's Beth Israel Deaconess Medical Center, confirmed that they were not aided by any international terrorist group for carrying out the attack.

According to the source, the preliminary interview of Dzhokar indicated that the suspected brothers could be categorised as self-radicalized jihadists. Dzhokar reportedly revealed that his brother wanted to defend Islam from the attack.

Investigating officers will now focus more on Dzhokar's statement to find out whether these details are true. Authorities have not given out any information regarding the suspects' motives behind carrying out the attack.

On Monday, Federal prosecutors booked Dzhokar under charges of using a weapon of mass destruction to kill. If convicted, the teen would face the death penalty.

During the brief initial court hearing at his bedside on Monday, Magistrate Judge Marianne Bowler found that the suspect was heavily sedated but "alert, mentally competent and lucid," CNN reported.

According to a transcript of the proceedings, Dzhokar, who sustained a throat injury presumed to have been a result of a suicide bid, responded to questions by nodding his head. His first word was "no" when the judge asked if he could afford a lawyer.

On Friday, the FBI dound Dzhokar hiding in a boat in a Watertown backyard following a gun fight with authorities. He sustained multiple injuries to his head, neck, legs and hand. He was said to have lost immense blood and was rushed to Beth Israel Deaconess Medical Center where his condition was said to be serious but stable.

Dzhokar was questioned by Federal agents after his Miranda rights were read out. On Monday, the Magistrate Judge Marianne Bowler once again reviewed the rights during the proceedings.

According to CNN, investigators were questioning Dzhokar at intervels in the presence of doctors. They are trying to retrieve information about the presence of any more bombs, explosives caches or weapons in their possession apart from the ones seized by the federal agents.

Dzhokar and his elder brother Tamerlan Tsarnaev, who died following an intense shootout with law enforcement officials on Thursday, were identified as suspects behind the Boston Marathon bombing of 15 April which led to the death of three people and injured over 170.

So far, the investigation shows that Tsarnaev brothers had no accomplices. However, the authorities are yet to confirm whether the two brothers were the only suspects in the case.