Boston bombing suspect Dzhokhar Tsarnaev has confessed and told investigators that his olrder brother Tamerlan was the driving force behind last week’s attacks, according to a report by CNN. Tsarnaev said that no international terrorist group were behind them, a U.S. government source said to CNN Monday.

Preliminary interviews with Tsarnaev indicate that the two brothers fit the classification of a self-radicalized jihadist, according to the government source. Dzhokhar Tsarnaev, wounded and held in a Boston hospital, had said that his brother – who was killed early Friday – desired to defend Islam from attack, said the source.

The government source cautioned that the interviews and what Tsarnaev said are all preliminary and that everything he has told investigators so far had to be checked out and followed up on by investigators.

A federal law enforcement official who spoke to CNN said that while investigators have seen nothing yet to indicate the suspects were working with anyone else, a lot of work remains before they can confidently say that no one else was involved. Officials would not comment on any motive or specifics Tsarnaev has communicated.

The 19-year-old Boston marathon bombing suspect has been charged with using and conspiring to use a weapon of mass destruction resulting in death, and one count of malicious destruction of property by means of an explosive device resulting in death. Tsarnaev was heavily sedated and on a ventilator at Beth Israel Deacconness Hospital. He was described as “alert, mentally competent and lucid” during the brief initial court appearance at his bedside on Monday, according to Magistrate Judge Marianne Bowler.

During the hearing the Tsarnaev communicated mostly by nodding his head, although he once answered “No” when Bowler asked him if he could afford a lawyer, a transcript of the proceeding showed. A public defender was appointed to represent Tsarnaev.

Investigators have asked the teenage suspect if there were more bombs, explosive caches or weapons beyond those found by police, and if anyone else was involved in the attacks, a source told CNN. Investigators go to Tsarnaev’s room every few hours to ask questions in the presence of doctors, the CNN source said.

Federal agents at first questioned Tsarnaev without reading the teenager his Miranda rights, under an exception to the rule invoked when authorities believe there is an imminent public safety, said a Justice Department official. By the time of the hospital room proceeding, government sources he had been read his rights and the Magistrate Judge Bowler reviewed those again with him.