LONDON -- Two teenage children of the suspect in Saturday's Texas synagogue hostage-taking standoff have been released from custody without being charged after they were questioned by British counterterrorism officers, authorities said.
The pair were detained in southern Manchester on Sunday evening, according to a statement from the Greater Manchester Police. Multiple law enforcement sources in the U.S. told ABC News that the teens are the children of the alleged hostage-taker, Malik Faisal Akram.
"Two teenagers, who were both detained in South Manchester, have since been released without charge," Greater Manchester Police said in a statement on Tuesday.
The teenagers were questioned by officers from the Counter Terrorism Policing North West in England in connection with the hourslong standoff between American authorities and a hostage-taker at the Congregation Beth Israel in Colleyville, Texas, about 27 miles northwest of Dallas.
The armed suspect claiming to have planted bombs in the synagogue interrupted Shabbat services on Saturday just before 11 a.m. local time, taking a rabbi and three other people hostage, according to Colleyville Police Chief Michael Miller.
British authorities also said an address in North Manchester was searched as part of the investigation of the hostage-taking incident but did not elaborate on whether any evidence was seized.
The suspect was identified by the FBI as Akram, a 44-year-old British national. Akram died in a "shooting incident" that culminated the 11-hour hostage standoff, according to Miller and FBI Dallas Special Agent in Charge Matt DeSarno, neither of whom provided further details. None of the hostages were injured.
Multiple law enforcement sources told ABC News that the initial indication is that Akram was shot and killed by the FBI team. The FBI said in a statement Sunday that its Shooting Incident Review Team "will conduct a thorough, factual, and objective investigation of the events."
A motive for the incident is under investigation.
Assistant Chief Constable Dominic Scally of the Greater Manchester Police said in a statement Sunday that counterterrorism officers are assisting their U.S. counterparts in the probe. Akram was from the Blackburn area of Lancashire, about 20 miles northwest of Manchester, according to Scally.
During the negotiations with law enforcement, Akram "spoke repeatedly about a convicted terrorist who is serving an 86-year prison sentence in the United States on terrorisms charges," the FBI said in a statement Sunday.
"This is a terrorism-related matter, in which the Jewish community was targeted, and is being investigated by the Joint Terrorism Task Force," the agency added. "Preventing acts of terrorism and violence is the number one priority of the FBI. Due to the continuing investigation, we are unable to provide more details at this time."
Multiple law enforcement sources told ABC News that the suspect was demanding the release of Aafia Siddiqui, who is incarcerated at Carswell Air Force Base near Fort Worth, about 16 miles southwest of Colleyville. Siddiqui, who has alleged ties to al-Qaida, was sentenced to 86 years in prison after being convicted of assault as well as attempted murder of an American soldier in 2010.
One hostage was released uninjured at around 5 p.m. CT on Saturday. The standoff ended hours later, when Cytron-Walker and the other two hostages executed an escape plan that included Cytron-Walker throwing a chair at the suspect and bolting to an exit door with his fellow hostages, the rabbi told CBS News.
Law enforcement sources also told ABC News that after arriving in the United States from London on Dec. 29, Akram stayed at homeless shelters at various points and may have portrayed himself as experiencing homelessness in order to gain access to the Texas synagogue during Shabbat services, sources said.
Biden told reporters Sunday that he was briefed on the incident at the Texas synagogue by Attorney General Merrick Garland. Biden confirmed that the suspect had only been in the country for a couple of weeks and spent at least one night in a homeless shelter.
Bide said investigators suspect Akham purchased a gun on the street. While Akham is alleged to have claimed he had bombs, investigators have found no evidence that he was in possession of explosives, according to Biden.
"This was an act of terror," Biden said.
ABC News' Luke Barr, Meredith Deliso, Bill Hutchinson, Aaron Katersky and Josh Margolin contributed to this report.