The FBI identified the suspectSaturday at a Colleyville, Texas, synagogue as Malik Faisal Akram, 44. Authorities said Saturday night that Akram had died, while all four hostages made it out alive.
Akram was a British citizen, the FBI said. He arrived in the U.S. two weeks prior to his death via New York City's John F. Kennedy International Airport, a federal law enforcement source told CBS News.
British police said late Sunday that the counter terrorism unit arrested two teenagers in South Manchester in relation to the Colleyville incident. They remained in custody for questioning as of Sunday night.
Two U.S. officials told CBS News that Akram did not appear on any U.S. terror watch lists, although they are still looking and working on name differentiations. The FBI is investigating if he had any help in the U.S.
Officials are also assessing the suspect's mental health.
Federal law enforcement investigating the scene have not yet discovered if any explosive material was found on the suspect, a senior federal law enforcement source told CBS News. Federal courts do not show a criminal history for the suspect.
Authorities said the suspect took four people hostages during services on Saturday morning, which were being broadcast on a livestream. The suspect could be heard ranting on the livestream, CBS Dallas-Fort Worth reports.
Four hostages were held inside the synagogue for hours, with one male hostage being released around 5:00 p.m. local time Shortly after 9:30 p.m. local time, Texas Governor Greg Abbott said the remaining three hostages were "out alive and safe."
Authorities said shortly afterward that the suspect was dead.
Authorities did not initially reveal a specific motive, but FBI Dallas special agent in charge Matthew DeSarno said Saturday night that the FBI believed the hostage-taker was "singularly focused on one issue, and it was not specifically related to the Jewish community." The FBI on Sunday said in a statement that throughout the negotiations, Akram "spoke repeatedly about a convicted terrorist who is serving an 86-year prison sentence in the United States on terrorism charges."
A source close to the incident had previously told CBS News that law enforcement believe the hostage-taker had asked for the release of, a Pakistani woman serving an 86-year sentence in federal prison for trying to kill U.S. officers in Afghanistan.
White House national security adviser Jake Sullivan called the incident an "act of terrorism" and an "act of antisemitism" in anSunday morning.
"We have the Department of Homeland Security, the FBI and law enforcement and intelligence agencies working intensively to get a full picture of what this person's motives were and whether or not there are any further connections," Sullivan said.
Homeland Security Secretary Alejandro Mayorkas tweeted Sunday that the "immediate crisis is over. Yet the fear of rising antisemitism remains."
"We must answer hate with action & ensure synagogues and all houses of worship are sanctuaries of safety, Shabbat and other days of faithful observance a time of peace, and America a place of freedom for all," Mayorkas wrote.
Mayorkas told CBS News that the Department of Homeland Security is "not aware at this time of any specific credible threat" against other places of worship or institutions related to the incident. He said federal law enforcement is "monitoring social media traffic" for indications of any inspired "copycat" events.
"We are monitoring social media traffic," Mayorkas said. "We have in the past seen incidents of violence be the subject of communications and efforts by those who seek to do us harm to inspire a copycat. But we are not seeing any specific, credible threat at this time."
FBI Dallas special agent in charge Matthew DeSarno said Saturday night that there is no indication of "any kind of ongoing threat." He said the FBI will continue investigating the hostage-taker, and noted that the investigation would have "global reach."
Mayorkas said on Sunday that he called the wife of Congregation Beth Israel's rabbi on Saturday. At that time, he also spoke with Sheikh Omar Suleiman, president of the Yaqeen Institute for Islamic Research institution, who was with the rabbi's wife and other faith leaders at the time.
"They presented a shining example of a fundamental principle: an act of hate, an act of violence that targets a particular group victimizes us all," he said.
Mayorkas confirmed that Beth Israel Synagogue has received Homeland Security grant funding through the nonprofit security grant program.
Rabbi Charlie Cytron-Walker of Congregation Beth Israel in Colleyville posted on Facebook on Sunday that he is "thankful" for the law enforcement and security training.
"I am grateful that we made it out," he wrote. "I am grateful to be alive."
Jordan Freiman and Jeff Pegues contributed to this report.
for more features.