"ABC News reported that the suspect is claiming to be the brother of Aafia Siddiqui, a notorious terrorist who is incarcerated at nearby Carswell Air Force Base. Siddiqui was sentenced to 86 years in federal prison in 2010 for conspiring to kill U.S. military personnel in Afghanistan. The suspect is reportedly demanding Siddiqui's freedom.

Foreign Policy explained more about Siddiqui:

[Siddiqui is] linked to al Qaeda and was convicted in 2010 of attempting to kill Americans in Afghanistan, would violate the administration’s policy of not granting concessions to terrorist groups, the officials concluded. It would also put a potentially dangerous fighter back on the street. Siddiqui ... who’s known in counterterrorism circles as "Lady al Qaeda," has been linked to 9/11 ringleader Khalid Sheikh Mohammed and was once on the FBI’s most-wanted terrorists list."

https://www.theblaze.com/news/congregation-beth-israel-hostage-crisis