Texas hostage standoff raising concerns about "copycat attacks"

The investigation into the gunman who held four people hostage at a Texas synagogue Saturday has increased concern among federal officials about possible "copycat attacks," according to an intelligence bulletin obtained by CBS News.

The joint bulletin was issued Tuesday to federal, state and local law enforcement partners by the FBI, Department of Homeland Security and National Counterterrorism Center.

Law enforcement sources say, and livestream audio of the incident reveals that the gunman, identified by authorities as 44-year-old British citizen Malik Faisal Akram, repeatedly asked for the release of Aafia Siddiqui, a Pakistani woman serving an 86-year sentence in a federal prison in Texas for trying to kill U.S. officers in Afghanistan.