Three U.S. officials talked to the Associated Press about the results of interrogating Boston bombing suspect Dzhokhar Tsarnaev on Monday.

The officials, who spoke on condition of anonymity because they were not authorized to discuss the investigation publicly, said Dzhokhar and Tamerlan Tsarnaev are not believed to have links to any terrorist groups.

Dzhokhar Tsarnaev was reportedly communicating with police through writing, unable to speak because his throat was injured in the shootout with police last week in which Tamerlan Tsarnaev, his elder brother and fellow suspect, died.

After interrogating the 19-year-old native Chechen, officials say the brothers were motivated by a radical version of Islam and anti-American sentiments. One of the officials called them aspiring jihadists.

Tsarnaev has been charged with using a weapon of mass destruction. If convicted, he could be executed. The interrogation yielded enough details to make “a strong case” against him, an official said.

The boys’ father, Anzor Tsarnaev, had told reporters from his home in Makhachkala, the capital Russia’s North Caucasus region of Dagestan, on Friday, that he believed his sons were innocent. “Someone framed them, I don’t know who did, but someone did,” he said in the interview, recorded on CNN.

He called the police who shot and killed his eldest son cowards: “Being cowards, they shot the boys dead. There are cops like this.”

He had talked to Tamerlan Tsarvaev, 26, following the bombing and before he was targeted as a suspect. He had told him to watch out for his younger brother and make sure he concentrates on his studies.

“Those are my kids, you understand,” the father said. In the end, “Justice should decide who is right and who is guilty,” he concluded, “I honestly couldn’t imagine who would do this.”

Brothers Seemed to Embrace American Life

After emigrating from Russia, the boys had seemingly tried to fit into American society, not giving much indication of what officials now say are radical, anti-American sentiments. The eldest joined a boxing club, the boys applied for American citizenship. 

They  emigrated about 10 years ago from Dagestan, the epicenter of an Islamic insurgency that spilled over from Chechnya.

Counterterror experts say the attack at the Boston Marathon is a classic pattern of young first- or second-generation immigrants reacting with violence to failed attempts at fitting in.

“There’s a sort of weird identity crisis,” said Kamran Bokhari, a Toronto-based expert on jihadism and radicalization for the global intelligence company Stratfor. “In many ways, these people are radicalized of extreme religious persuasions in the West that’s not even reflective of what’s back home. So they’re sort of frozen in time, where they’re rejecting the reality in front of them.”

The brothers’ uncle, Ruslan Tsarni, said he thought the motive behind the attack was likely “hatred to those who were able to settle themselves.”

“Anything else to do with religion, with Islam—it’s a fraud, it’s a fake,” Tsarni told reporters. He said someone possibly “radicalized them, but not my brother who just moved back to Russia, who spent his life bringing bread to the table.”

The father of the suspects will travel from Russia to the United States “to clear up many things,” he said Sunday. The suspects’ mother, Zubeidat Tsarnaeva, said on Monday that he will arrive Wednesday. She also said they will try to bring the body of their eldest son back to Russia.

Chechen Terrorists’ Statement

Vilayat Dagestan, a jihadist group linked to al-Qaeda and operating in the North Caucasus, issued a statement on Sunday concerning speculation that the Tsarnaevs could be linked to the group.

Tamerlan Tsarnaev had traveled to Dagestan and Chechnya in 2012. The terrorist group neither confirmed nor denied a connection to Tsarvaev, according to a Haverford College-sponsored Global Terrorism Research Project report.

The group said, however, that it is “at war with Russia,” and “not fighting against the United States of America.” U.S. intelligence officials told the project that they were investigating a number of terrorist groups in the region, but as officials told the Associated Press on Monday, it seems the brothers acted independently. 

The United States has historically taken a hands-off approach to Chechen affairs, according to an article posted on the Humphrey School of Public Affairs at the University of Minnesota website. An analysis of presidential statements shows President Barack Obama had not publicly mentioned Chechnya before the Boston bombing. The last time any president mentioned the region publicly was in 2005.

Bill Clinton had said in 1994: “It is an internal Russian affair, and we hope that order can be restored with a minimum amount of bloodshed and violence.”

The Associated Press contributed to this report.