threat to america, too. nigel was the counterterrorism chief at the time of the 9/11 attacks. >> it wouldn't be the first time it happened. 9/11 was planned out of hamburg. >> using europe as a base. >> exactly. >> fighters returning from syria to the uk regardless of claimed intentions can be arrested. citizenships yanked. 16 were blocked in january. authorities are also counting on in fighting between militants. zawahiri announced al qaeda is coming with one group for being too extreme. >> the ambiguity of being a foreign fighter in this conflict are becoming slightly harder on the ground. >> one more thing working in the authorities' favor, some of the jihadis never get home. over 20 britons have been killed in syria along with reportedly the american we showed you. he's said to have died shortly after making the video. shannon. >> thank you, greg. a kinder, gentler vladimir putin in the run-up to the